Scanning is fast; it took only a minute on my test PC. SpeedUpMyPC reports its results in three categories: Speed Tools, System Tweaks, and Junk Files. Under Speed Tools, SpeedUpMyPC mentions a CPU Manager. The Manage tab goes into a little detail about what it does: It's an applet that keeps an eye on your CPU usage so that processes with memory leaks can't use up all that CPU.
Here's the big problem: After scanning, once you click on the Manage tab to read up on the feature you're about to install, the app appears to lose the scan. However, you can click on Scan Results to get them back. This solution is workable, but not obvious. Ideally, SpeedUpMyPC would have that extra info within the scan tab itself.
The other problem is that this extra info is available only for the Speed Tools category. System Tweaks listed 45 improvements in my scan, and had a one-line description for each, but didn't go into more detail at all. The first one, "Disable unnecessary services," is especially problematic. It lists 10 unnecessary services without saying what they are, and I'd definitely like to know which 10 it's disabling and why it considers them unnecessary. But there's no way to find out that information. The vendor did say that in the manage/system tweaks section, you can select which disabled service to undo, after the fact.
Another System Tweak is "Speed up shutdown by automatically closing non-responding applications." Especially in Vista, applications frequently go non-responsive and usually clear themselves up after a few seconds. With this enabled, the application will stay non-responsive until you choose to close it, then SpeedUpMyPC will close it instantly instead of the long wait usually accompanying this function. This seems like a good fix.
However, the bottom line is that it's difficult to trust that an app like SpeedUpMyPC is doing everything you want, unless it tells you exactly what that is. Until then, you're better off with a few well-chosen tweaks that you can perform by hand. Note: The demo version of SpeedUpMyPC has various limitations. According to the developer, the demo version will enable one active rule, the first two tweaks that apply to the PC being used and the first junk file section on the PC being used.