What is a "PC optimizer", if you don't mind me asking? Are you referring to those applications that I've mostly (only) seen for Windows, that "get rid of garbage and tune your computer to run twice as fast, including registry cleaning"? If so, then it's about just that..removing unneeded files, cleaning registry (note: Linux doesn't use registry the way Windows does, here such system-wide data is stored in other ways), turning off unneeded services (see /etc/rc.d or /etc/init.d) and so on..not sure if such "ready" programs exist on Linux, but if they do, you probably will find them by searching your distribution's specific forums.
If there were such apps, I take it they don't do much. I never noticed a big difference on Windows either, but there it's another story (at least somewhat), as the system actually does collect garbage at an incredible speed sometimes
But instead of apps there are surely "tweak guides", sometimes distribution-specific, that contain information -- written by somebody who hopefully tested the tips before writing about them -- on how to make your Linux (<distribution name>) run and/or boot faster. Typically they ask you to remove graphical splash screens (hmm..I wonder how much it speeds up with today's hardware not to load them?), recompile your kernel to drop off modules you don't use and so on. More speed would probably be possible to gain by recompiling all software, but that's probably too much for an average user anyway
If you meant some other sort of "optimizer", describe it in more detail..but if you meant what I mentioned above, you're probably better off searching for tweak guides than software.
There probably isn't "PC optimizer", since the hardware can't much be optimized..it's the operating system and/or software you have to modify to get more out of the whole package.
