Robert Scoble tried it (see TechCrunch a couple of day ago).
Register writes (seen through Steve O'Hear):
Many social networking cheerleaders see this type of business as their
own AdWords goldmine, while failing to appreciate that a general
ongoing interest in “sports” is nowhere near as valuable to marketeers
as a Google search on a particular day for “Adidas football boots”.
It seems, making money out of your virtual friends is not too easy.