I'm on a 56k and I listen to mainly classical music, so I'm really sensitive to the encoding.
Most of the stuff I DL from Napster has been done with crappy software like Xing that uses a low pass frickin filter or something, because it just kills classical music. Plus the snaps and pops in many of the tracks I DL.
Easier to rip my own CDs and have full control over the quality. Napster is good for previewing stuff that I don't have though. Then I just go buy the CD and rip away!