Things that WILL impact performance are:
1) Add RAM! I cannot stress this enough. Paging memory to hard disk is sssssssslllllllllllloooooooooooowwwwwwww!!!!!
2) Disabling indexing service will improve overall explorer.exe performance SLIGHTLY, but will dramatically DECREASE file search performance. If you make regular use of the Windows search feature (or use programs which use search internally, like Microsoft Office), then to disable the indexing service is to shoot yourself in the foot.
3) Unloading certain startup programs, particularly those which do background indexing (malware, certain media indexing programs, etc…). DO NOT disable everything in the taskmanager! Most services are dormant until needed.
4) Defrag your hard drive periodically. The slow people do this rarely, if ever. The fanatics do this waaaaaaay too often. Once a month is usually adequate.
5) Disable themes, 3D desktops, and all other cool but useless gadgetry you don’t need. If you like to run software like WindowBlinds on XP, or Aero on Vista, there may be no hope for you!
6) Stop trying-out every performance tip you read about! Most are of no use whatsoever. And continually messing with Windows’ guts will INEVITABLY crash your PC. But, hey… If you have no problem re-installing Windows, then GO FOR IT!

Realize that ALL programs load and run only as fast as your hardware will let them… And that nothing… NOTHING… is going to make your circa-1999 computer run Call of Duty 4!

Just read the article, and there is only two of these “myths” that i don’t think are myths : the “clean the registry” thing and the question of disabling unneeded services.

Well, the first is to my opinion not well considered : registry cleaning in itself doesn’t give any performance boost, but if you follow the cleaning process by using a registry defragger such as NTregopt or Auslogic Registry Defrag, here you gain a noticeable boost in overall system speed (after reboot of course), because it actually reduce the size of the registry (by removing the gaps left by the keys removed). The gain can be more or less noticeable though, depending of the reduction that occurred, but a 20% reduction (that I had quite often on XP because I like testing software, and many uninstallers have the very bad idea of not being complete…) is very noticeable. Automatic registry cleaners can do lots of false positives though, so I think safer to use a manual approach : I just use regedit to suppress the keys associated with programs I uninstall after the uninstaller completes if it left some, so I know what I delete. A good registry editor can come in handy here of course.

For the services, sure caution is needed here for not disabling useful services, but I gained a lot of memory back this way, both in XP and Vista (200Mo), and all works so far. There are some good guides on the net that explain what service stands for, and just disabling the ones that are not needed for what you do with your computer free some memory. By security I don’t “disable” services though, but just change them to “manual” state, which explain maybe why I have no problems as they can start if needed (except a few like “Remote registry” for obvious security reasons). This said, I sometimes check the services running and didn’t notice any of the ones I set to manual to be running…so I suppose they really are unneeded for what I do.