Take just now as an example. Me minding my own business and catching up on newsgroups. I pull up my friends page (using Semagic), and nothing appears to happen. Then XMPlay starts cutting out (while playing an OGG from the local disk). The CPU is just ticking over, so this is obviously Not Good.
Oh, and the disk light is on solid.
Turns out that one of my disks is slowly going bad, and as well as reporting bad block errors to windows went and hogged the IDE bus for a bit (causing a timeout in Windows). Looking at the SMART status with Everest shows numbers that while aren't themselves that bad, they could be better (like being zero in the case of sector reallocation).
Well, it could be worse. The disk isn't making nasty "click-click" sounds yet.