FB is attracting more and more people I know who are top notch technically - Alex Feinberg, Simon Marlow, to name a couple. With Google the impression is that the really cutting edge people are the 'old guard'- Ghemawat,Dean, Norvig, Horzle (spelling?), even Guido Van Rossum.
Here is one more FB edge: From a purely local (Indian) viewpoint, FaceBook hires ultra sharp people for its US offices, vs Google mainly hiring into the local (Bangalore) office, which is a horror politically (i.e manager competence and behavior) and technically, and then (by HR policy) making you wait 2 or 3 years before you can transfer. I really wish someone at Google HQ would do some Augean stable cleaning here.
As of today, for a sharp Indian dev, it probably makes more sense to apply to Facebook than Google.
But then OTOH Larry and Sergei are more inspiring leaders than Zuckerberg. So ...
(due disclosure: spoken as someone who has no intention of working for either company, and has no axe to grind for either company. just stream of consciousness, and it is the middle of the night here, so apologies for any incoherence)