Originally Posted by r34lg33k

true that !!

Whichever Os you have doesnt really cahnge the core problems.
Depending on the current definition of "Optimized"...

[hardware/os]
-"top" and "ps aux" will give you a good idea on ANY platforms.
-Watch for I/O, hard drive read & writes
-Check for processes with elevated Cpu priority
-Check for zombie processes
-"who/w" can help to show if remote shell are running.
-do not run services as 'root'
-check for memory leakage
-check for programs in 'trace' mode
-check for swaps and its usage
[...]

[software]
-Apache: with ErrorLevel in Debug mode is bad, mmm'kay
-Mysql [if used] check the "show processlist;" output and connections.
[many other but those are almost everywhere]
[...]

[scripts]
it is easier than it should be to bring a beast to its knees using simple php,perl scripts especially some pop extensions.

-ONLY- after making sure of the above and a couple more can you start considering getting more RAM and upgrading CPU, or else the basic problems stay

this is a very short list and it should change according to your setup. Your Hosting company might help, but bringing an outside consultant will almost always bring a new perspective/experience in the game.

glad to help