Windows is a closed source system. Developers of tuneup utilities and registry cleaners do not have the core code of Win 7 and are not working on definitive information, but rather they are going on past knowledge and experience, most of which is not applicable to Win 7. Automatic cleaners will usually have to do some guesswork.
There is almost no tweaking that can be done to Win 7 to speed it up. The system is designed to diagnose itself and take care of itself which it does remarkably well. Win 7 maintains itself and that includes the registry.
Registry cleaners are pure snake oil. At best they do nothing except use resources. At worst, they can mess your system up, slowing it down, and even crash it. There is no utility out there anywhere that can speed Win 7 up and improve its performance, at least not at this time.
Modifying registry keys incorrectly can cause Windows instability, or make Windows unbootable. No registry cleaner is completely safe and the potential is ever present to cause more problems than they claim to fix.
Registry cleaners cannot distinguish between good and bad. If you run a registry cleaner, it will delete all those keys which are obsolete and sitting idle; but in reality, those keys may well be needed by some programs or windows at a later time.
Windows 7 is much more efficient at managing the registry than previous Windows versions. Even if you use the CCleaner registry to delete keys left over when uninstalling programs, these few keys will not make 1 millisecond's difference in performance. If you run CCleaner or any other registry cleaner and do not know precisely what you are doing, you will have problems down the road. There are no gains to be had from using a registry cleaner and the risk is great.
Forget all the "wisdom" you learned about XP. Windows 7 is not XP and does not manage the registry the same as XP.
This isn't to say that the system does not need to be maintained. Uninstall programs that you don't use, delete unneeded and unnecessary files. Defrag your hard drive. But don't screw with the registry unless you are an in depth expert in the Win 7 registry.
Most of the time, the cure is a clean install. Using a program such as Ccleaner is fine to get rid of old and unnecessary files. A tuneup utility is not only unneeded, it can actually harm your system. Don't use them.
