I had no luck with it at all, with 6 years of PPC I could not utilize facebook to make it worth while. I must admit I was hired to test Facebook for specific campaigns/industries (financial & insurance etc). Needless to say results were not desirable.
from what I see, majority of the ppl on facebook just go there to waste time,socialize , gossip and play games.
Knowing what ppl do on facebook we should be able to exploit/utilize these certain areas and their stupidity by advertising dumb things like Quizes,surveys, personality shit etc.
For personal tests I tried couple of ZIP/Email Submits / giveaways and clickbank products with limited success.
Facebook and SE PPC can not be compared at all- it's apples and oranges. PPL on Adwords for example are activly pursuing/searching for the product/service you advertise and facebook they do not, it's like banner advertising.
Besides that I did not crack their "approval process" , it appears almost as if some blind monkeys where pushing buttons, deciding to approve or disapprove ads.
I would imagine you can profit greatly from facebook if you do your homework first. A lot of solid research and targeting is needed. To me it is not worth it as I have proven methods and projects that require my attention.
If you got a voucher/coupon for it go ahead, if not make sure you set limits and watch the budget like a hawk.
good luck