Depends on what you are expecting from it.
It only helps with load/save times from/to disk.
I wouldn't bother with ordinary drives. Better off just buying a Raptor - which will be about as fast as most ordinary drives in RAID0.
I've personally dropped from RAID0 Raptors to a Spinpoint SP2504C, and dont really notice any difference except in Windows boot time (and i dont really care about a few seconds difference on an event which only happens once a day anyways).
M