[kingpotnoodle]

Fast, quiet, gigabit networking, good support for various RAID levels, ideally 4+ drives, low power consumption, web interface, does neat things like download management, audio streaming for you (for instance on my file server I run the open source Subsonic), sends alerts about hardware failure via email at minimum.

Now a cheap linux server like mine can do all the above, so it's gotta be low cost to complete with that, and to get one up on such a machine it'd need things like hot swappable drives, small size. very, very high uptime, quick boot times, easy and quick setup.

Like the above poster it would also be very nice to have security controls, different user names to access different segregated areas, and remote authentication as well, access across many protocols (SMB, FTP etc).

I also like the idea it automatically backing up, but for me off site would be the only really good way as it's RAIDed already to another drive attached via USB seems superfluous... so it should have remote sync capabilities with online storage providers or with another NAS in another location, and use your internet bandwidth sensibly, during off peak hours - if necessary to build up the backup over several days.