The registry cleaner seen in CCleaner is a farse to make the hard drive cleanup tool look more impressive. Besides the Windows cleanup tool available for use after a fresh installation of Windows a period run of an actual registry cleaner that works never hurts to see anything lingering when an uninstaller fails to remove all entries.
An easy to use and still freeware tool would be one like Eusing found at
http://www.eusing.com/free_registry_...ry_cleaner.htm