OK, OK, having 5,000 songs is not that much. I've heard people with collection in the 15,000s and over. The eMule freaks, downloading 24/7 without ever actually listening to anything can easily have collections in the 50,000s.
However, I never downloaded a copyrighted song from eMule, even though my collection does not entirely consist on original CDs. Actually I downloaded a lot of albums from the Internet... namely Creative Commons music from Jamendo.
Some info about my collection (some statistics taken from the Amarok player, since around June 2006):
Total songs: 5015 - Commercial: 3944 - Jamendo: 1055 - Other CC: 31 Total playing time: 1 week and 6 days Total file size: 22GB Song playcount: 10910 Different artists: 627 Different albums: 413 In MP3: 1562 In OGG: 3468
There is some mismatch (5030 songs, as counted from actual files (all OGG and MP3 files I have in a given directory) vs. 5015 songs as counted from the Amarok collection), but I see no easy way of filtering the 15 rogue files (update: I did, some time after writing the post).