It's amazing how much better your computer starts acting when you wipe it out and start over fresh. All the assorted junk that you've installed that's left it's entrails all over your machine. Software that you thought that you'd use but has done nothing but take up space since you put it on. Little quirks that drive you nuts but aren't quite bad enough to make you want to fix them. All of that gone with a fresh OS install. Only the programs that you really use installed back on the machine, migrating only the preferences for the stuff you use.
It's a great release and in my case resulted in another 20Gb of free drive space to play with (not that I was hurting). I know that I should do that more often (with as often as I'm installling and uninstalling things) but it's such a pain. Making the backup, waiting for all the installers and updates to run, figuring out where the preference files live for each application. And all of this spurred on with the discovery of an unused firewire drive and a couple of random lockups.