When used judiciously, CCleaner (I still prefer the original name, Crap Cleaner) is anything but "an automated tool", unlike a number of the other software previously mentioned. That isn't to suggest that most users' don't treat it as one - many even seem to think it's some kind of anti-spyware/malware tool!
Seriously, guys, spend a little time actually studying the CCleaner options and how it works - or just uncheck the top 2 to 4 boxes in the Registry section ... it's useful as a shortcut to "doing it manually", usually giving you a few leads to work with and a bonus 'open in Regedit' option on the right-click.
When first run on a problematic PC, the Registry section often highlights areas where the User/Owner has been messing around, programs that have been installed/removed, etc.
The major problem comes long after removing default but empty entries in the Registry - many simply cannot be added back, and the (future) installers that make use of them are not always programmed to recreate them, only to populate those default 'slots'.
