Windows is a closed source system. Developers of 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.
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.
We have seen the adverse effects of registry cleaners and registry defraggers in the Crashes and Debugging Section. 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.