It works fairly well. It's also quiet --- no whiring like a jet engine. Actually very quiet. Except a few quiet clicks made when writing or reading. I have tested up to 12 tracks of audio East West Gold instruments with a heavy load of notes. It works flawlessly. It looks like I could add another 12 and still not have any problems --- but then perhaps someone else will try that.
The internally installed 74 gig Raptor works with my new SATA only dual 2ghz Mac. If you have another format type for drives like IDE you are going to need a card.
I could get it to crap out with the Bosendorfer sample set --- about as heavy a sample set as you can get. I had to palm the keyboard back and forth vigorously to get clicks and to get it to shut down.
I use a 3Ware RAID cage to house my raptors.O.S. +Apps. on 360G,Convolusion impulses on 740G, and sample libraries on 1500X. The cage was uneeded for they are fairly quiet for 10k rpm HDD's. The new X has 16MB cache 150GB. I was running GigaPulse Pro and samples on the 740G, and was quickly running out of room, it came at the right time.