Nice. Not exactly a monster of capacity, woefully enough there are 4TB USB 3 disks that may even be faster than this (and of course there's the wd velociraptor duo that connects via Thunderbolt), but if you can get suitable PATA to SATA adapters at a reasonable price, or build a new backplane... there's a lot of opportunity there.
If you want to run it in tower orientation, you may consider something like this:
http://www.xrackpro.com/XtroVERT-Xserve-RAID-Stand-s/2.htm
Marathon Computer (the company that made iMac and PowerMacintosh G3/G4 rack mounting kits) used to make a pair of classy feet for using xserves and xserve raids vertically, but they seem to be defunct now.
Tangent: Vertical/tower disk arrays are one of the things I often feel is missing from server vendors these days. Ah well, I am probably one of the few folks who would like a vertical/tower version of the HP D2600 or Dell PowerVault MD1000/MD1200.