With all the noise about Microsoft’s $41 billion offer to buy Yahoo, I dropped the ball on posting about a chat I had about a week ago with Slide’s Max Levchin (pictured here) about the recent $50 million investment that valued the widget maker at an astonishing $500 million.

To say I was dumbstruck by the market value, given that the profitless start-up has only about $10 million to $12 million in annual revenue and a still unproven business plan, would be wrong.

Incredulous, yes. Gobsmacked, indeed. Feeling like I was back in 1999, most definitely. But not dumbstruck!

Thus, I queried the always voluble Levchin, who agreed to talk to me readily (no Jerry-Yang-cave-dwelling behavior for this 32-year-old Web 2.0 serial entrepreneur!) about the investment by two old-line institutional investors–Fidelity and T. Rowe Price–and its implications for Slide.

“We’re like a teen in our clock cycle,” said Levchin about what he thinks the money means to Slide. “Now, we have to figure out how do you get a job and work in the real world.”

It’s juicy quotes like this that make it easy to see why the young geek–whose last score was PayPal, which was sold to eBay for $1.54 billion–has become such a press darling, especially combined with his restlessly complex mind, curious intellect and a much longer view than your average dot-com entrepreneur.

And that’s why it sometimes feels effortless to start shaking your head in rapt agreement, even if you don’t agree at all, as he laid out the reasoning behind his contention that Slide and its giant bag of cash will now emerge from puberty fully mature.

This, despite the lack of profits in the here and now, which Levchin did not dispute. “We could start to turn toward profitability with not too much of a stretch,” he said, with a strong trace of his Ukrainian roots in his stilted speech patterns that make him sound a bit like a robot.

Instead, Levchin said he was more interested in the opportunities that he saw emerging for Slide–which has grown to almost 150 million monthly visitors and several billion monthly page views, by offering to consumers its range of software to make slide shows, engage in SuperPokes and do other often pointless widgety things.

“We were [operating] super-thin, but with a whole lot of ideas, so we had to prioritize what we had to do,” said Levchin, who said he did not plan to raise more money until recently. “We later brought up to the board that we were seeing all this growth in places.”

That was true on social-networking sites like MySpace and Facebook, where Slide was grabbing enormous growth, although Levchin has been trying to aim future increases off those platforms to other social networks like Bebo and Hi5, as well as internationally on its own.

To do that required money and lots of it, and from non-VC investors to give it more credibility beyond the bubbly go-go tone of Silicon Valley.

So using Allen and Co., a well-connected New York investment firm, Slide grabbed a pair of firms that reeked institutional, Fidelity and T.Rowe Price, which Slide still does not name.

“I thought it was best to raise money from people people who invest for a living and have some combination of risk-taking and knowledge,” said Levchin, who later noted that he would have thought the investment was frothy, if he could not convince anyone but VCs to hand over cash at the lofty $500 million valuation.

“I think it was flattering that these were not jokers,” said Levchin of his new investors.

He said he stopped potential laughing by unveiling a steady pipeline of revenue from sponsorships, impressions and clicks of all kinds.

More importantly, he noted, he began to outline a new way of reaching consumers more efficiently that was “not the bleak world of brand advertising.” Still, that does mean more consumer brand links, like the one Slide made this week with Kodak to make it easy for users to move around their photos.

But the heart of Slide’s promise, like a lot of socially oriented Web companies, lies in manipulating the information it is collecting from consumers. That essentially means using an intense version of e-metrics–data of when, how, where and why consumers click on things.

“It’s no surprise that we are mathematical … and we study data carefully,” said Levchin. “We’re building a predictive model that is close to perfect … where we can say what the revenue per user will be.”

Well, we’ll see about that–along with obvious privacy issues, the jury is still out on the effectiveness of social networking and its payoff, and also on how spammy such advertising can become. Last week, for example, Google blamed its weakness in its recent quarter on lack of progress in monetizing these platforms.

In an article in The Wall Street Journal today, for example, Kevin Delaney noted: “Since advertising on social-networking and video-sharing sites is still largely experimental for marketers, it could be more vulnerable in an ad-spending pullback.”

Thus, Levchin’s investors are betting Slide will surmount those challenges.

Happily, he discounted any revenues that Slide has made selling ads to other widget companies to improve their rank on sites like Facebook.

In fact, Levchin agreed that it was a bit of a “Ponzi scheme” and not a big part of Slide’s future. “It’s a little business that is going to go away,” he said.

Levchin hopes, of course, that does not describe Slide, which he has said he wants to get to a $2 billion valuation, somewhat based on his last experience at PayPal.

“I have said I have a chip on my shoulder and that it is PayPal-motivated … but I have no black line in the sand about it,” said Levchin. “But I do want to see that I can do it again…Call it obsession, call it megalomania, but I am definitely not crazy.”

Indeed, of all the players in this trip down the rabbit hole, Levchin is probably the most sane of all. After all, he’s got the money in the bank.

It’s Bubble Time!

As BoomTown broke the news in its post earlier today, Slide grabbed a big pile of cash from new investors–$50 million from Fidelity and T. Rowe Price–which puts the value of the company at $550 million.

In our post, we said the San Francisco start-up, whose widgets are among the most popular on Facebook and MySpace, was completing a round of funding that could value it at many times a multiple of its most recent $60 million to $80 million valuation.

The investment from the pair of private equity funds gives them a 9% stake in the maker of widgets and other social-networking applications.

Allen & Co., the media-connected New York-based investment firm, helped Slide execs in raising the latest round.

Don’t think we did not notice that the venture investors already in Slide did not pony up more funds at this–let’s just say it, shall we?–crazy valuation.

But it is noticeable that such mainstream investors are jumping into the giant pool of Kool-Aid that the social-networking industry has been swimming in over the last year.

Slide’s last round–an investment of $20 million–took place in November of 2006 with investors that included Khosla Ventures, BlueRun Ventures, Founders Fund and the Mayfield Fund.

So Slide’s investors, of course, were smart to get in on the ground floor to take advantage of the bubble that is expanding at alarming rates.

The ground-zero of that trend came when Facebook got a $240 million investment from Microsoft that valued the company at $15 billion.

Of course, while garnering revenues, neither Facebook nor Slide has the kind of business yet to deserve being worth this lofty amount, except for the fact that investors are counting in its potential and recent quick growth.

Slide’s business plan includes making money from selling premium versions of its widgets, as well as selling advertisers on its large, although disparate, audience.

The company calls itself the “largest personal media network in the world, reaching more than 134 million unique global viewers each month and 30% of the U.S. Internet audience.”

But the company recently said reports had put that number at 144 million, excluding its 50 million users on Facebook. Its competitors include other widget-makers like RockYou.

Slide makes a wide range of software, called widgets, that have been attracting many millions of users each. They include everything from slide shows to a program called SuperPoke that allows a user to, well, poke another in a super way.

A lot of Slide’s current growth has been through taking advantage of the huge spike in users first at MySpace and now at Facebook, which is promising, but also not certain.

To say that we have seen this story of fast growth, insane valuations and then the inevitable drop-off would be an understatement.

But Slide Founder and CEO Max Levchin and his team consider the company to be a new kind of distributed content and application company that is not dependent on large platforms like Facebook and MySpace and has huge potential.

Minor blogging annoyance: Of course, in a fit of pique since we revealed the funding without their help, Slide hand-fed the details of the deal to the New York Times and BusinessWeek, both of which somehow forgot to link to our post that said Slide was landing the deal. (Brad, Sarah: Please, please don’t tell us you figured it all out on your own this morning over eggs.)

UPDATE: A New York Times deputy tech editor just wrote an email to tell me its reporter already had a “previously scheduled” meeting with Slide about the deal–like I said, hand-fed!–this morning, which “inspired” its post and did not know of BoomTown’s news of the funding (even though it was up since 12:06 a.m. and noticed by everyone else, including Slide). Also, they had the hand-fed details! They did! I admit it! I went hungry, since I did not agree to an embargo! “In light of this we didn’t feel that a link was warranted,” he wrote me.

But we’re not bizarrely ungenerous like that, so here is the link to the New York Times story, in which Slide’s Levchin said his company makes Facebook and MySpace worth using. (And here is the BusinessWeek link too.)

“It’s impossible for social networks focused on scaling the network itself to build all the niche applications that bring people and keep people on these sites,” Levchin said, noting Slide widgets “add the bulk of perceived value to the consumers of these Web platforms.”

He also said he would use the money to expand its repertoire, but said Slide would try to develop in-house.

But others close to Slide said this was not exactly so, and that the company would also look around for good acquisition targets, using stakes in the newly valued Slide as currency.