The Web is littered with Windows tips and tweaks, may of dubious quality and accuracy. Eric Vaughan’s TweakHound is one of the few sites that actually tests and rejects the bogus tweaks. If you’re thinking about making some changes to your registry because some random site told you it would speed things up, I suggest visiting the Bad Tweaks page first:
Many of these once worked in some version of Windows and virtually every tweak guide and program use these tweaks. My guide also used to contain some of them. It has taken a considerable amount of research and testing to come to these conclusions. While others have incorporated these into other guides and tried to pass it on as their own work I’ve done the investigation and benchmarking (and AFAIK I was the first to publish these en masse on the web). I’ve Googled up one side of the net and down the other. Sometimes I think I’ve seen every page at Microsoft. I’ve hosed installs, applied and removed settings, and spent more time tracking the registry than I care to admit (far more than I would like my wife to know about!).
Nicely done, Eric.
Ed Bott 
Some of the most useful “tweaks” of all are the ones that take place between the ears. There is more useful performance information in Ed’s recent tips regarding Task Manager than I have found over the Internet over the last five years. The key is understanding what affects everyday performance, both positively and negatively. This is primarily what Task Manager is for, at least as Ed has taught me how to use it.