We took over a company some years ago with 100 SQL2000 dbs. CHECKDB was never run. I found two that had minor corruption that would have not allowed them to upgrade to 2005. I got one of them fixed and one I could not. It wasn't a serious issue in MSFTs eyes and it was going away so I didn't bother. I got checkdbs scheduled and low and behold within a few months one failed. I got it fixed but the point was it happened.