In recent months, Facebook has been working hard to recruit talent from Google. For example, Google lost Android Product Manager Erick Tseng to Facebook a few months back. Rumor has it the The Big G is now starting to take the situation seriously, and is making some serious counter-offers to keep employees from going to Facebook.
TechCrunch has spoken with one former Googler who was offered a substantial 15% raise, quadrupled stock benefits, and a $500,000 bonus (!) to stay for one year. This particular developer, and others, have still taken the Facebook deal for one simple reason. Facebook is expecting an IPO soon. They haven't been making it official, but sources claim that Facebook is telling prospective employees that their individual stock benefits could be worth $100 million in just a few years. Now that's walking around money.
How big is the problem for Google? According to LinkedIn, at least 118 Google engineers have left for Facebook so far. It's not likely to damage the Google brain-trust, but it's not a trend you want to see.