Also for your information: Most of those "classes" are full of completely useless information, or they state highly obvious things, like limiting the number of programs you have running.
Generally speaking, there are about three things that will speed up your computer, regardless of operating system. In order of effectiveness:
1: More RAM
2: Faster CPU
3: Limiting the number of programs running
Those are pretty much the only things that will have appreciable long term effects on computer performance that can be controlled by the user. Everything else is either just a parlor trick, or a fleeting gain.
So all the tips about defragmenting, disk cleanup, registry hacks, etc... All of them are either completely untrue, have negligible gains if any, or apply only to highly specific cases, most of which you will never encounter.