I did 175000 words on my HTC mobile phone/PDA - it worked really well though more 2 hours on it in a go tends to wear the end of your thumbs!
Another big advantage it has over the a laptop is you can use it upside-down! Perfect for when laying in the tent.
However the keys are now being to act up - so trying to source a new membrane, or a blue-tooth portable keyboard, or an eeePC. Just seen a mates eeePC 900 looks a perfect bit of kit - except for the upside down use.
At £330 it ain't cheap though. My mate had the eeePC 700 for two days before taking it back to the shop as it was too basic.