Last year I did a Facebook case study (actually, a mini-case study) which I forgot to post here. It shows the incredible efficacy of real estate lead generation on Facebook (or really, in any niche) – if you know what you're doing, of course. As shown here, we were able to create very strong response in a very short period of time, for next to nothing in cost.
NOTE: similar results on Google Adwords would have probably cost five times as much – if not ten. And since Adwords is nothing like Facebook ads running on Facebook, there is nothing like the long term or residual effect you get on the world's biggest social networking platform. If and until Google more effectively ties it's ad platform into Google+ – and Google+ starts to rival Facebook (it's not even a close second right now) – it will have nothing like the effect of Facebook ads.