I was sceptical about business advertising on facebook, and as a big fan and user of adwords, I thought it only fair to give it a try.
We tried a variety of campaigns over 3 months, and although cost wise, its pretty cheap, it resulted in very few clickthroughs, and not a single conversion.
So for me personally, I see facebook or similar as maybe a branding possibility, but not commercially viable if I'm expecting to see a return/conversions.
I think this is mainly because of the audience, as already mentioned (unless your selling to a young audience) but also in the way people use and interact with the site.
Your there to talk to your muckers or play games, so your attention is focused. Many users logon, respond to their messages, and log off, lets face it, most are youngsters in the workplace diving on quick before the boss catches them. So they wont notice or be interested enough to click on adverts, which the traditional surfer who is wondering and meandering may do.
Adsense or similar tends to be displayed on more static or informational sites, with the adverts displayed at potential exit points, and advertising here, for us at least, is a lot more cost effective.
