When I originally built the PC I'm using, I set it up to dual boot Windows 2000 and Linux (I think I had a Mandrake distro at the time).
Last year my hard disk developed bad blocks, and started making occasional electric-shaver noises. I bought a new 100 GB unit, and installed both in the machine so I could transfer files over at my leisure. I loaded Red Hat 7.3 on the new disk and put the old one on the second IDE adapter. After a few minutes of futzing around, I couldn't figure out how to make GRUB boot Win2K, so I left it like it was, thinking I'd come back to it "one of these days".
This weekend I blew away the Windows partition, realizing if I hadn't booted to Windows in a year, I probably never would again. So now I have a spanking clean 30 GB