I had the same thoughts when I first got my iPod--I was too afraid to delete everything off the hard drive when I'd synched up, even though I have the original CDs, just because it'd be such a pain to re-rip *everything* if anything ever did happen to the copy of the library on the iPod.

I finally broke down and got a small, cheap, external hard drive that I use for the library. I don't have to worry about accessing it unless I'm ripping a new CD, and I don't have to worry about hogging up 60GB of "regular" space on my machine with yet another copy of music that I already have both the source CD and iPod copies of.

Slightly wasteful and redundant, probably, but it made me happy.