I have read several books on Windows 7 written by Microsoft 'MVPs.' These people are supposed to know what they are doing. In exactly one book, the woman who wrote the book recommended registry cleaners, but she was an IT pro. Not one of the other people in their books recommended registry cleaners. Some said don't use registry cleaners at all. Some said that if you manually have to work in the registry to back up the registry and be extremely careful, and not mess with the registry unless you knew what you were doing. And one guy who was a Microsoft MVP said he used CCleaner but only to clean out unnecessary files and he did not recommend the registry cleaner in CCleaner. He said that CCleaner was better than Microsoft's Disk Cleanup built into Windows.
Microsoft used to have an online antivirus scanner that included some registry cleaning. But it was real conservative in what it did. And Microsoft has since dropped the registry cleaning in their latest online scanner.