I guess the question should be "why are you focusing on the registry as the possible source of your percieved lack of speed problem?". When your PC is running more slowly than it was, first look at what you programs you have running. Look at the process list in the task manager. Look at msconfig (or directly at the places in the registry that msconfig is making it easy for you to manipulate).
Adaware, spybot, Micro$oft antispyware. Install them all, update them all, run them over and over until they run clean.