inicholson
Nope...not all.
Oh hang on...it MIGHT be a problem if your friend has purchased the music from the iTunes store. If that's the case, then the mp3 file will have a 'digital rights management' code associated with it.
What this means, is that your mate can play it on his PC, but when you come to play it on yours, you'll be asked for an iTunes userid/password which has to match the account used to download the original track.
However, if your mate has simply ripped music from CDs, then there's no issue. iTunes won't know about that.