I have used icons from various sites that says they are free for commercial projects. This includes sites like iconspedia where anyone can upload stuff.
I am very cautious and whenever I use one I take a screenshot of the entire website including its URL and the license. I do the same with free photography from sxc, etc.
It occurred to me when obtaining graphics in this manner, just because something claims to be free on a website does not make it so. If I used a “free” graphic that turned out to be under a more restrictive license, what position would I be in legally?
Am I being paranoid? I must say, I've been in the game for years and have never known anyone get accused of anything like this—and they're way less careful then I am.