I have a friend that setup a far better system IMHO for far less money. He purchased four 750 gig super fast drives. Then he built them, using the Apple supplied Raid software (disk utility) as mirrored and striped array! So four drives, two mirroring for protection while striping for speed. Cost about $500 (popped them in his existing four drive bays in his MacPro).
While we're on the subject, this is the set-up I use for performance when reading, batch processing and writing large blocks of files. I am using 4x WD 640G Caviar non-enterprise drives*. The first two are striped for the OS and and the second pair are striped with a thin outer 128 G partition for scratch and the rest for my working image files. With this set up, I can read from the working file array and write to the OS desktop and get sustained transfer speeds of 150MB/s, which is pretty decent -- C1 literally screams as I batch convert a block of my P45+ raws. And yes, having my CS scratch on a stripe really improves performance when manipulating large files that need scratch. Also, a FWIW benchmark: CS4 opens in less than 3 seconds from the striped OS array.
* At present, the WD 640's are among the fastest currently available 7200RPM SATA2 non-enterprise drives THAT RAID WELL
. Hitachi 1TB non-enterprise spinpoints benchmark very fast for 7200 RPM drives too, but myself and others have reported problems with them in RAID configurations. And the WD 640's are dirt cheap now.
But that isn't reliability, it is performance... And I recommend you have a solid back-up strategy if your main files are on raid arrays or single drives. My current strategy is I back up my working image files to the Drobo (which also stores my historic image files) and then back that up to individual drives stored offsite. A bootable copy of my OS is backed up to a partition on a 5th drive stuffed into the lower optical bay of the MacPro box and connected to one of the extra SATA ports on the MB -- that operation is scheduled weekly using Carbon Copy Cloner, and yes I've needed it. This drive also carries a Time Machine partition which I've rescheduled to run twice daily (instead of hourly) simply to serve as tertiary back up of the OS, documents, mail and downloads.