MDDs are pretty awesome. You can upgrade them to be pretty respectable and have loads of expansion. I just built up my MDD. I got a dual 1.42ghz CPU (and overclocked to 1.58ghz on stock voltage) with copper heatsink from work (for free) and I had a FW800 logic board I threw in a while ago. Popped in an Airport Extreme and bluetooth card, DL Super Drive, 2GB RAM, ATi 9800 Pro 128MB video card, 2 USB 2.0 cards, FW400 and FW800 cards and 4 hard drives. You can put in a SATA card and theoretically put 12TB worth of storage (2x 2TB drives in each hard drive bay and two more in the optical bays with mounts) and it'll make a pretty nasty file server.