Facebook advertising is hot. Get on the train.
Cost per click is super low, and conversion rates are much higher then Adwords.
This wont last forever. Just like Adwords got to expensive, Facebook will as well.
I have also noticed click volume declines over time, so as someone mentioned keep the ad creative fresh, or maybe remix the keywords.
If your running a thin site, or a site without a unique design you might have some trouble getting approved. Certain industries seem to have auto ban's as well.