Executives at major media companies and advertising agencies are defecting to web start-ups in increasing numbers, attracted by some combination of equity and autonomy. Here’s a closer look at who’s left, and gone where.

Executives now at startups:

Mark Kingdon
Was: Chief Executive, Organic
Is: Chief Executive, Second Life
Moved: April 2008

In a somewhat puzzling move, Kingdon announced his departure from Omnicom-owned Organic in New York on April 22. Puzzling, because industry opinion is split: On one hand, many view Second Life as last season’s trendy (and virtually licentious) new web company; others see the opportunity for Kingdon to take a leadership role to legitimize and advance the virtual world industry, which is fledgling to date aside from MTV’s recent success with endeavors like The Virtual Hills.

Sean Finnegan
Was: Chief Executive, OMG Digital
Is: Chief Media Officer at Vibrant Media
Moved: January 2008

In a surprise move, Finnegan stepped down in January from OMG Digital, a unit of Omnicom Media Group that handles media buying for Omnicom clients in over 70 countries. With a high-visibility role at ABS Ventures-backed Vibrant Media, Finnegan is expected to juice agency buy-in of Vibrant’s in-text video ad delivery system. Vibrant has been around since 2000 and profitable for the last five years, according to co-founder and CEO Doug Stevenson.

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Jon Sedlak
Was: SVP - Eastern Region, AOL
Is: SVP of Sales and Strategic Alliances, Vibrant Media
Moved: January 2008

Sedlak, a sales veteran with past jobs at AOL and Time Warner, also went to Vibrant in January.

Paran Johar
Was: EVP Digital Marketing - North America, MRM Worldwide; Managing Director, MRM Los Angeles
Is: Chief Marketing Officer at JumpTap
Moved: January 2008

Johar joined JumpTap in January after a long run at MRM Worldwide, a division of agency conglomerate McCann Worldgroup, where he ran digital strategy for heavyweight clients like General Motors and Microsoft. Why the jump? Johar says he wanted to move from helping clients shape their digital marketing strategies, to helping shape the mobile marketing industry itself. Jumptap is a formidable mobile search, ad and content provider with white-label with agreements with over a dozen carriers in nine countries and a recent extensive content deal with NBC Universal. They took in $22mm in a financing round two years ago led by Valhalla Partners, and including Redpoint and General Catalyst Partners.

Bill Masterson
Was: VP - Agency Relationships and Sales, United Online
Is: EVP at Media Rights Capital
Moved: January 2008

A familiar player in Madison Avenue media circles, Masterson moved a lot of experience and relationships with him from United online to MRC, an independent film studio associated with Los Angeles talent agency Endeavor that is using $400 million in backing (from AT&T, advertising conglomerate WPP Group and Goldman Sachs) to promote films like “Babel.” (More here from NYTimes ).

Adam Gerber
Was: VP - Ad Product and Strategy, Brightcove
Is: Chief Marketing Officer, Quantcast
Moved: November 2007

Gerber joined Quantcast in November of last year and is expected to draw high-profile Madison Avenue attention to Quantcast’s internet ratings system. Based on their data collection methodology alone (which keeps coming out with