These things are great
I've got an older (6 months old) 1TB version and they are great. Plug it into your router and you have a wifi hard disk with access anywhere in the world, providing you have set up your network properly.
The older version (mine) has a 500MHz ARM processor with 32MB of RAM, this limited the transfer rates, so hopefully this new version has a more powerful chip looking at el reg's benchmarks.
These things run Linux, check out:
I have mine fully AES encrypted (the big partition, not /) and setup as an nfs server, samba server, UPnP media server, printer server, rsync server. I can happily play 5 different films at the same time on a wired PC and 4 wireless laptops with no pause or skips. Need more laptops to fully stress test it.
Once you have ssh access these devices are a hackers dream, you can fool around with them to your hearts content. Nice community on the wikidot forums as well.
I haven't had any problems with connectivity like other are reporting. Set your router to assign the thing a static IP address, make sure everything is on the same workgroup if your using windows. NFS is still faster and nicer.