nomas, I agree to the fact that it's probably more common with teenagers. I don't know too many people around my age (20-25) who have fwb. Most of the guys and girls would never get together with a friend. I guess it really depends, some people think that friendship and sex should not mix because one of them, and a lot of times both of them, end up ruined. I think girls for most part, like you mentioined, look for something more meaningful even if it starts out as something like kissing without being in a relationship. In general, for a lot of guys it's more like an experiment and it doesn't happen as often that the guy would want to consider something more serious.
-to be nobody but yourself in a world which is doing its best, night and day, to make you everybody else means to fight the hardest battle which any human being can fight; and never stop fighting.- e.e.cummings