I spend a lot of money on Facebook ads, and I'm still on the fence about them. I pay for clicks and have gotten some big sales, but I'm using it more for 'brand awareness'
A couple of the reasons I like FB ads:
*They are easy, I find it less complicated than AdWords
*You can really target. Since I'm selling wedding invites, I can target based on relationship status "Engaged" as well as select for 'likes' for sites and blogs of my target group (DIY, etc.)
I'm keeping my eye on it. I have my Google Analytics set up so that I can trace sales back to their source. I get a lot of traffic from the FB ads, but so-so sales, so my campaigns have yet to pay for themselves. I'm going to let it run through the summer and if they don't perform more than just bringing in traffic, I'll probably stop.