No it's not esoteric. As far as I know, there are quiet a few people, facilitating the SheevaPlug as NAS -  at least one of them with RAID.

I have built a RAID5 with 5x1T WD Greenpower, using SheevaPlug and 5 USB Cases.
I noticed that StarTech 4x USB/eSATA-case, but thought it's way overpriced so I bought 5 pretty simple USB-SATA-cases.

Running with raid5, lvm, dm_crypt, and cxbiker's 2.6.32.6 , I get ~5MB/sec over SMB - not impressive but sufficient for HD-videostreaming.