There's a really simple freeware utility published by PC Magazine. It's called InCtrl5. It can keep a record of all changes made to the system's file complement, and all alterations made to the registry hives and even the ini files. To find out what wasn't removed by an uninstall procedure you'd have to go through the list it generates manually to see what was left behind. It can definitely be worth it, particular when you're talking about registry entries.
The utility works very well, and I trust myself to use it far more than I would trust any of the automated third party uninstaller applications.
If you're interested, go to
http://www.pcmag.com/utilities/ and click the "more utilities" links. I believe the utility is located about three or four pages back into the archive.