One caveat, do not use it on a new install of XP Media Center Edition.
I don't know what the deal is, but the two don't play nice.
I made that mistake a few weeks ago. I was helping out my in-laws by doing a data backup and N&P of their old system. I didn't want to spend all night doing updates, so I just tossed in my WSUS disc. Everything seemed to install just fine, but when it rebooted, it was stuck in a reboot cycle. I ended up having to boot into safe mode and then use System Restore to uninstall all of the updates. Bah! In this case WSUS cost me more
time, but I won't forget that you shouldn't use it on XP Media Center in the future.