- Illegally downloading a some tracks of dubious quality from the Internet via one of the various P2P-type systems out there
- Copying one or more of your friends' entire music libraries
As of a few days ago, Apple has sold 350 million tracks and about 15 million iPods (each of which can hold hundreds or thousands of tracks). It is obvious that most of those tracks are not purchased from the iTunes Music Store (which is the only place to buy tracks for the iPod).
The real question is how many tracks users actually "own" and how many they don't own.
Really, the argument could be made that iPods are doing far more damage to the record industry than anything else. But you don't hear anybody saying that.