I think MK808 is a much better deal at the same price.
There are some interesting sticks out if the i/o limitation is ok but the MK808 is obsolete & slow.
Having said that, probably the best home NAS could be built out of an HP Microserver N54L: 250$ for an Amd Turion "small" server that supports up to 8GB of RAM (16GB sometimes), it has 4 (non-hot-swappable) disk slots (but there are guys who have installed more using 2.5 disks and the dvdrom slot).
there are plenty of forums and sites showing how to do it, the only downside is that it is bigger (but 4 slots) and it consumes more power
EDIT: I'm still deciding which way to go in order to substitute my old Seagate Dockstar running Debian (and with a single old 2.5 disk attached to one of the USB ports)