I'm not sure how useful it will be. That will depend on how open it is to new applications. If it can run Vim, I'll definitely be coughing up to buy one :-).
Basically, it's a mobile phone "companion" ... a device with a larger, 10" display that can sync with your phone via Bluetooth, so you can read/write e-mail on a decent sized screen, with a much better keyboard.
It has a custom version of the Opera web browser, which can access the internet via WiFi, if you're near a hotspot, or via Bluetooth, through your phone. It can also work with Office documents.