Facebook employees that joined the company in the last few years will have a much higher tax rate than employees that joined prior to 2007. The early employees will be taxed a rate of 20%-25% (the long-term capital gains tax), while employees that joined later on and were issued restricted stock units will face a tax rate of 45% when the company goes public later this year. Inside Facebook has the details, but I imagine this will lead to interesting conversations at Facebook.

[Source: Inside Facebook]