Inserting advertising into a phone conversation would ruin the experience (more so than an ad on a website). But it would probably be noticed!

You are probably right to an extent- but a lot of times people are browsing FB to waste time. If they are looking at the profile of some girl they like, and an ad shows up for the new album of one of the bands she likes- could that not potentially be an effective ad? (This could be a friend, who has a birthday coming up, and FB could suggest presents based on your friends preferences). I really think that FB just needs to adapt their ads better. I hope they get it figured out and prove everyone that thinks they aren't worth 15 billion wrong!