Someone mentioned renaming as a way to help this... but renaming would stop many people too. Fileservers function by showing people the filename, then people request that file. If the fileservers changed, for example, Some Band - Some Song.mp3 to blahards.exe then people using the fileserver would have no friggin idea what they were downloading.
Plus, it would inconvenience the fileservers. If you were giving people illegal files for free to begin with, would you really sit down for five hours and change all your files for their convenience?
And heres another idea, cuz I'm chock full of em today ^-^ What about a kind of quota? When have you ever sent like, more than 10 files in an hour? Fileservers do that easily, especially broadband ones serving mp3s. If they couldn't send more than 10 an hour..well, you face the same workarounds but the filesharers that compulsively upgrade their software would be slowed down for a while.