Have you tried to promote affiliate products/services through myspace and facebook? What is th success rate? Is the traffic generate form these social network site consider legitimate or not?
It works for very specialized things. You can advertise legitimitely on Facebook through their flyer system.
Posting affiliate links on myspace or facebook is a good way to get your affiliate account terminated.
You can do it, but there are so many better ways to get much more rabid buyers then through Myspace and Facebook. However, even though the visitors are not likely to buy as say... PPC, I do know a few dudes yanking about $50K a month out of Facebook and Myspace combined. To me though, it just sounds like too much work and too much spamming. However, if you got a method down, and a lab of outsource monkey's it can be done. I'd just make sure you are driving them to a squeeze page so you can continue to sell to them once you've extracted them from Facebook or Myspace.