I've had an old hard-disk lying around for a while. It's the smaller of the two that I had when my hard drive failed and at the time it was reporting a lot of errors. Now, though, I've hooked it back up before deciding whether to dispose of it and it works fine with the disk check reporting no errors.
The best part is that it's only an 80GB disk and I've now got a 160GB and a 200GB disk installed, but I can still fit all of my data on there including full back-ups of all of the sites (Skins@HWT is the better part of 1GB!), installs of all of the Dawn of War games, and a virtual machine with Windows installed, as well as all of my music, documents, applications and other files!
Why do people need hard disks in their desktop that are approaching 1TB? My entire disk usage is less than 50GB. The only way I'll need something that big is if/when I create a MythTV box and I start recording TV to watch later or converting my DVDs to video files!