I've gotten into a ~6 month routine of doing this. I have a 40 GB HD that gets the main windows install. After that I have a 160GB drive I dump all my program installation files, pictures, music, ect. Finally a RAID setup that has my games installed into for faster load times, and an extrenal backup as well for ensuring my pictures and music don't get lost.
Every 6 months XP will lag uncontrollably, and I'll start the ritualistic reinstall of Windows and all the applications I love and need. The C drive gets wiped clean, and everything gets a fresh install. 30 mins to get Windows started, 30 mins to install all the hardware drivers, and another 30 mins to setup all the other visuals like background, screansaver, internet bookmarks, and various desktop shortcuts.
I know what you're thinking. That's a lot of effort, and what if I forget to save some of my important stuff in the reinstallation? Well the alternative is that you wait til Windows completely bugs out and you get BSODs on startup, requiring you to do this anyways. I've had that happen and it sucks. Everyone should know how to backup their important stuff anyhow. Because if you don't you're just waiting for trouble to hit.
As inconvenient as it is to spend a few hours reinstalling windows, I find it more annoying to sit at a computer that takes 2x longer to load everything, freezes up when you don't want it do, and potentially crashes and corrupts the files you thought you could save forever.