I believe this acquisition was also a play to acquire more engineering talent. Through this acquisition they acquired John Carmack which is a fairly famous engineer amongst the tech community. That component alone strikes me as an incredibly awesome PR move in terms of recruitment.

As far as I'm concerned Facebook is the only competitor to Google at this point. Facebook is just trying to keep pace. I assume they're going to do many awesome things in the near future that aren't necessarily aligned with their current business model in order to keep up that pace.