Not really....RAID 0 mostly helps STR (sustained transfer rate). Most of what people do involves opening/closing a bunch of small files, so RAID 0 doesn't really give hardly any benefit. Plus, like BSA said, it doubles your chance of data loss. RAID 0 is more for video editing, where you have big files to deal with.
Get a new WD 640gig or Samsung F1 1tb, that will be the best cost effective upgrade. OR get the $300 VRaptor, it's the fastest HD right now. (the WD and Samsung are ~10% slower, and 1/3 -1/2 the price)