I'm looking for something with:
* 6 SATA ports
* Runs current Ubuntu from a USB stick
* Can serve NFS over gigabit ethernet at reasonable (>20MB/sec) speed
At the moment I'm using a whole Q6600 with 8G memory for this - my last-but-two desktop PC. This is sub-optimal because it uses quite a lot of electricity, and constantly tempts me to run sieving jobs or aliquot-sequence searches on it rather than just having it sit and serve NFS, DHCP and DNS, and ftp and http to the outside world.
http://linitx.com/product/13104 is my current thought.