Up to now, I have only used any P2P tools for three things - downloading ISO files of Linux distros, grabbing tracks off an album before purchasing - to ensure I like at least 4, and instead of ripping all my tapes and LP's to mp3 (it was taking too long) I just grabbed them from Kazaa.

So one legal use, one a bit iffy, but ending up with me buying more CD's - so keeping the RIAA happy anyway, and one probably legal use (depending on jurisdiction, I guess)