I've had a Netgear ReadyNAS NV+ for about a year, and yesterday I bought and installed a second one. What do I think?
These boxes are about the size of a toaster, and have room for four discs. I've put Seagate 2TB discs into them, and to be specific, 4 x Seagate ST2000DL003-9VT166 into the latest machine. The ReadyNAS is a SPARC based linux machine, but you'd never know because the interface is web-based and easy to use.
I put the four discs into their drive cages (5 minutes), connected the power and network, turned it on and went to bed. By this morning it had checked the drives, updated its firmware, built a RAID 5 array (technically it's something else, but it has RAID 5 functionality), and created two shares. These were CIFS (SMB) and AFP, but it also can create shares based on NFS, RSYNC and FTP. There is also functionality around http and https, which I don't use.
They are interesting boxes, since they prioritise sharing heavily - don't bother trying to use the management interface while pushing its gigabit ethernet interface. These are not meant for more than a handful of users if you push them.
Plenty of other people have reviewed these machines, so I won't go into detail other than to say that it offers Time Machine backup for my Mac Mini, RSYNC works perfectly, it keeps the discs at a few degrees above ambient temperature, the discs are hot-swap, they're quiet, and a pleasure to use.
This machine will eventually replace my ageing Windows Home Server v1, which I will miss, but its habit of killing discs is becoming a bit old. I have pulled a disc out of the ReadyNAS and it responded as advertised.
One major point: if you run one of these (or any other consumer RAID 5 array), have a spare disc ready - the moment a disc fails you should replace it, because if another disc goes bad or is already marginal you need to get that new disc in immediately.