Create a System Restore point if you're in doubt first then allow it to clean it up. Then restart your computer. If nothing is broken, then CCleaner did it's job without damage. If it went horribly wrong, just use Safe Mode to revert back to the restore point.
Usually CCleaner's registry cleaner is not really aggressive and can clean up the registry without any damage. You won't really notice any difference in performance unless you defragment the registry which is something CCleaner does not do. Defragmention of the registry comes in tools that usually cost money though.
[Edited by Neo7, 6/26/2010 12:59:19 PM]
I do use Tune Up 2010 which has the Defragment Registry function, but it doesn't detect erros CCleaner does and vice-versa.
Cleaned it, rebooted the PC, so far so good.
But I don't know how to run that Visual Studio 8 program, so I don't know if it did affect something.
Thanks for the replies.
[Edited by ArchDuke, 6/26/2010 3:35:51 PM]