Turned up in the post today, been playing with it this evening.
THe unit arrived with firmware 2.17.14, and it told me there was an update. Before I updated it, I checked in the Twonky web config page, it was running TMS 4.4.9.
I updated to the latest firmware, it's now running 4.4.12.
So far extremely impressed with the unit. The LCD on the front panel is VERY neat, it shows the status of the device, and you can instantiate backups of a desktop PC, to the device with a single frontpanel button press. It gives you pie charts of your diskspace usage and types of media stored.
The best bit, is the flash based management and playback interface. VERY slick and works really well. It's intuitive to use and very speedy. It's clearly manipulating Twonkymedia server through it's RPC interface thou Makes we want a flash based interface on TMS now thou....
If anyones in the market for a NAS that takes big disks and can do mirroring (this one can handle 2TB mirrored), then this would be a smart choice. Obviously I haven't seen what other vendors are offering, but I can safely say if I had paid the asking price for one of these, I would be pleased with my purchase.