By default, Windows Media Player encodes your music collection using your machine's unique key, so that you can't share, loan or give away the tracks you rip to your machine. What that means is, if you have some file-system or OS corruption and reinstall from scratch, then restore your music collection, it will be unusable. You won't be able to play the files. There's a backup utility that'll preserve your license keys, but if you fail to employ it, you're SOL -- MSFT's position is that you need to start over from scratch at that point, re-ripping all the CDs in your collection. Speaking as someone with 30GB of MP3s, ripped from over 1,000 CDs in a process that took days, I gotta say, I'm glad I'm an OSX user. Link Discuss (via On Lisa Rein's Radar)