However...would I be asking for trouble using something esoteric like the above as my file storage in a Sheevaplug based file-server setup?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 18.104.22.168 , I get ~5MB/sec over SMB - not impressive but sufficient for HD-videostreaming.