to Matt and fiddler2007
ccleaner allows for full registry backup to file, before you scrub it. So, in case something goes bananas, you can always go back to previous reg settings.

P.S. I never had a problem with aggressive part of it before. I used it for about 8 years now. The interesting thing about it, it allows to block / uninstall certain Microsoft and other wonderful adware processes that are not removable by standard programs->uninstall.