One of Yahoo’s highest-ranking premium advertising sales execs–David Dickman, VP of West Coast sales–is leaving the company, people familiar with the situation said.

Sources said Dickman, who will leave Yahoo at the end of the month after three years at the company, is reportedly going to Time Warner (TWX) unit Warner Bros. to work in digital sales.

Well liked at Yahoo (YHOO), Dickman was impacted in a sales reorganization done in the spring.

At the time, Atlanta-based regional sales VP Mitch Spolan was named to lead Yahoo’s North American field sales, consolidating its display ad sales groups, which had previously been split between the East and West Coasts.

Before that, Dickman ran the Western sales and another exec the Eastern sales, serving big display advertisers. The latter exec took over agency sales, while Dickman remained running sales on the West Coast, reporting to Spolan.

Dickman’s departure comes after another top Yahoo display ad exec, Todd Taplin (pictured here), left last week. He was regional VP of sales in New England and Canada, responsible for big Yahoo display advertising accounts like Fidelity Investments in Boston.

Taplin–who was also well regarded at Yahoo–took a job at Collective Media in New York, as its new Chief Revenue Officer.

Flux at the Yahoo ad sales group in the U.S.–which accounts for most of the Internet giant’s revenues–will be closely watched by Wall Street right now since it is also charged with selling premium search ads for both Yahoo and Microsoft (MSFT) under the recent deal they struck. Yahoo is also aiming to turbocharge its premium graphical ad sales business.

BoomTown just could not resist making the obvious literary pun on the debut of Peter Kafka’s new daily blog, MediaMemo, on AllThingsD.com.

(He is pictured here.)

For those who were not dragooned into reading existentialist writers in college, I am referencing “Metamorphosis,” about a man who turns into a bug–except that the process is fraught with so much more meaning.

And thus it will be in Peter’s column, as the most excellent writer and reporter plunges into the topic–as he writes in his first explanatory post–of “the ongoing battle between the established media business and the technology that is reshaping it day by day.”

It is transformative, to say the least, from someone who will lead you through it with the kinds of standards, accuracy, great writing and insight that I hope you have come to expect from this site.

While Peter’s impending arrival to ATD was announced in mid-September, he actually debuts today and will be posting many times daily.

As I have previously written, Walt Mossberg and I have long wanted to bring in someone located on the East Coast and away from the echo chamber that Silicon Valley can be, because we both feel the ongoing digital revolution is taking place over a number of key industries all over this country and the world.

With extensive connections across the media, advertising, entertainment and tech sectors, Peter will be doing original reporting, getting scoops, doing interviews, making videos and providing much needed and clear-headed analysis that he is so well-known for.

Peter has been working at Silicon Alley Insider, most recently as its managing editor, since mid-2007. The first hire at the start-up tech business analysis site, he has focused on enterprise and beat reporting, as well as breaking news.

Previously, he spent 10 years as a reporter and editor at Forbes and Forbes.com covering media and technology. (You can read more of his bio here, along with his ethics statement.)

Walt and I are thrilled that Peter is coming onboard to join the rest of the strong ATD team, which includes: John Paczkowski, author of the rocking Digital Daily column, who formerly wrote the award-winning blog, “Good Morning Silicon Valley” at the San Jose Mercury News; and Wall Street Journal reporter Katherine Boehret, who writes the most excellent weekly Mossberg Solution column.

And we hope you will soon find–via following Peter regularly–why we are so very excited to welcome MediaMemo to the site.

Although we did not raid the offices of Silicon Alley Insider and “steal” Peter Kafka, as the fanciful SAI kingpin Henry Blodget alleges–had it been a raid, BoomTown would have properly hog-tied Blodget so he could not make such spurious allegations!–it is true that SAI’s current managing editor (pictured here) will be coming to work for us at AllThingD.com soon.

Indeed, Walt Mossberg and I, as well as the rest of the ATD team, are thrilled that Peter is coming onboard at the end of October. He will write a daily still-unnamed new media blog from New York City.

Walt and I have long wanted to bring in someone located on the East Coast and away from the echo chamber that Silicon Valley can be, because we both feel the ongoing digital revolution is taking place over a number of key industries all over this country and the world.

Peter was our first choice and has been on my must-read list since I began this blog. He is sharp, witty, confident and has the kind of reporting and writing chops that we think are key to giving readers high-quality, standards-based content they can trust.

With extensive connections across the media, advertising, entertainment and tech sectors, Peter will be doing original reporting, getting scoops, doing interviews, making videos and providing much needed and clear-headed analysis that he is so well known for.

Peter has worked at SAI since mid-2007. The first hire at the start-up tech business analysis site, he has focused on enterprise and beat reporting, as well as breaking news.

Previously, he spent 10 years as a reporter and editor at Forbes and Forbes.com covering media and technology. There he launched two tech columns, coordinated the video staff and represented Forbes on industry panels and in TV appearances for CNN, BBC and CNBC.

Peter was also a staff reporter with City Business in Minneapolis and a staff writer for the Minnesota Real Estate Journal in Bloomington from 1993 to 1997. Earlier, he was a stringer with the Milwaukee Journal and the Milwaukee Sentinel in Madison, Wis.

He holds a bachelor of arts from the University of Wisconsin and resides in Brooklyn, NY.

More importantly, Peter is a newly-minted father, which should give him more practice in prolonged sleep deprivation needed for his blogging.

He will begin at ATD on Oct. 27.

Along with Walt and me, Peter joins senior news editor John Paczkowski, author of the rocking Digital Daily column, who formerly wrote the award-winning blog, “Good Morning Silicon Valley” at the San Jose Mercury News, and Wall Street Journal reporter Katherine Boehret, who writes the most excellent weekly Mossberg Solution column.

We hope you are as thrilled as we are that Peter is coming soon to the ATD site.

(And if you want a little taste of Peter’s work, here’s a post he did yesterday on an appearance by Time Warner’s Jeff Bewkes at the Goldman Sachs media conference and another on Rupert Murdoch of News Corp. [News Corp. is the owner of Dow Jones and of this Web site].)