"... Facebook would sell the property to a REIT or other institutional investment group like a state pension fund. The investment group would then enter into a longterm lease with Facebook as the tenant of the campus. This arrangement would allow Facebook to move to a bigger headquarters while at the same time extracting a big lump of cash."
Now, a few hundred million bucks is no small amount, but Silicon Alley Insider has FB with $2 billion in its checking account for 2011.
That cash could be for the new digs, a stock buyback, server farms ... and buy some startups.