My desktop computer was becoming very unstable, so, after four years, I decided to repartition (bye-bye Linux!), reformat my hard disk, and reinstall Windows XP. My previous installation was over Windows 98, so it will be interesting to see whether a fresh install is more stable than an upgrade.
My data is backed up to CD-R's, and most of my correspondence is done using webmail, so there were no problems there.
I also use Gmail to archive my important documents, as I trust the people at Google to look after my data far better than I ever would.
The only thing I lost were my RSS feeds (which I forgot to back up), although I did export the list of subscriptions, I just have to find them. I think I'll start reading RSS feeds using an online service as well, for the reasons listed above.