I'm not sure about the A3000 case issue, but I have three of the SCSI card readers and I can boot any 3.x OS I want (probably 1.3 and 2.04 as well). I can boot or back up to the inserted card quickly and silently; I can't boot to OS 4.1, but I can mount the card and read from it. SD cards are pretty slow for large back ups.
