I've heard this rumor in the valley about a month ago: seems like many people in Google are packing and moving to the next gold mine: Facebook.
With the Google stock at an all time high, the chance of hitting the jackpot at Google right now is slim to none. The "bonanza" (i.e. people becoming millionaires) is way behind us.
Facebook, however, has its future ahead of it. And getting Facebook options now, after the Microsoft's investment inflated Facebook's valuation to $15bn is akin to getting Microsoft stock in 1981.
And then I ran across this Techcrunch post. Not only does it confirm that numerous key people left Google for Facebook, and that 2-4 people a month keep migrating, but it bemoans the fact that Facebook "poached" TechCrunch's product manager, Ben Meyer, by promising him some options (and, one would assume, a better salary than TechCrunch - a startup, could offer).
Michael Arrington, TechCrunch's CEO doesn't take this lying down - he actually asks for any negative Facebook story people can provide, so he could publish it on TechCrunch's blog.
Poaching has been practiced for years. There's actually a whole branch of recruitment called "headhunting" which specializes in locating people in managerial and executive positions at company A, digging up their salaries, benefits and career goals and having company B top those wishes. This way you get an experienced person, with a proven track record. And if s/he was (relatively) underpaid, you get them at market value.
(By the way, there's a link to my resume on the upper right side of this page. Poach me, Facebook! ).