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.

While Wetpaint’s $25 million new round of funding was leaked to one and all under embargo until 12:01 am EST today–including BoomTown, so don’t assume any of us report our little hearts out on all these bits of news–what the press release did not disclose, sources said, was an intriguing new investor: Fidelity Investments.

What’s interesting about this wrinkle is that it is yet another validation in the Web 2.0 world from a large traditional institutional investor.

Fidelity, with T. Rowe Price, already plunked down big bucks to invest in widget king Slide in January.

Seattle-based Wetpaint, which allows users to make wikis and social-networking sites easily, has raised about $40 million in total so far. New investor DAG Ventures led the current round, which included investors from two previous rounds (Frazier Technology Ventures, Trinity Ventures and Accel Partners).

BoomTown could not determine exactly how much Fidelity kicked in to Wetpaint in this round, although it did pony up almost half the new $50 million Slide investment.

Wetpaint, which also announced a new embeddable product called Wetpaint Injected today that sounds cool, says it will use the additional funds to goose its collaborative–or as we like to call it: wikified–social publishing platform.