Yeah I think they will be ok. The Mac Air i use now with Win7 64 gets about 5 hours of real world use which isn't bad, and that's with a more power hungry i5 and larger screen to power. iPads get more battery life but they also do much less, I always had to keep a laptop around and switch to that because the iPad was inevitably not enough. Price wise ultrabooks are supposed to be hitting the $799 range this year, so I figure the Surface Pro can't be priced far above that. I'll buy if they are $1000 or less. Since they replace three of my other devices that still makes it a good deal to me, as I can sell those other 3 devices to fund a single Surface Pro and still pocket some change.
Now I'm hoping many of those awesome pc point and click adventure games get re-released on the Win8 app store with mouse and touch support, that way I can play them anywhere on any device. Good times