A lot of resistance against facebook these days, but you cannot argue it's a behemoth. I've met people in poland, serbia, turkey, DR, and they all have facebooks and many are active on it.
FB has momentum in many developing countries. As myspace (hypothetically) gains ground in the US, UK, etc. (and lets face it that's where these ads will be targeted) fb will continue to grow. IMHO all it needs to do now is not screw up and continue what it's been doing - being a meeting ground for people and their interests.