I havent actually got to use it much yet, they sometimes have them on display at JB Hi-fi have a look there. The pen has some cool features though, you dont even have to actually touch the screen you can press a button and point (i think, some guy was demonstrating) also its multi touch so you can iPhone style finger things (apparently those features arent so great).
You'd have to look up more about pen though, i think you can get it on Windows 7 now and Win7s meant to have lots of cool tablet and touch screen features. I think it has around 3.5 hours of battery time with the defualt batery, but you can get better batteries and the guy i bought mine off lets you customise it as much as you like including the type of battery.
If you have tons of cash though, maybe consider getting a Fujitsu tablet? Everyone seems to agree they are the best. They cost a lot and specs arent good though. Another option would be to get one of the newer Atom-based netbook tablets which are a lot like the hp tx2 only cheaper with netbook specs.