My PC is 7 years old and runs WinXP SP3. I'd reached the point of this being the last thing to try before a clean install. My PC was very sluggish and kept hanging in IE7. After I used it, it had turned my PC right around. I've now been using this software for around 3 months. It now runs like new.
However, having said that, I would never run any system cleaner, disk defrag or reg cleaner without first setting a 'System Restore Point' and the equivilent with 'ERUNT' as a fail safe.