I always inventory unless I am doing the good old "nuke from orbit" reformatting. Plus, it pays to burn to DVD/CD anything that is important to you.
That's what I did...nothing on it wasn't already backed up. Except drivers, games, etc, to reload....
It bums me out the way games and so forth have to hook into the Windows Registry to work correctly. I'd rather just have a "Documents" folder and a "Games" folder that I can just copy to an external HDD, then reformat/re-install Windows, then copy the "Games" and "Documents" folders over with no hassle.