I'll admit that the iPad's lightness is a nice feature, but not a necessity. Also, I am not a power lifter, and for comparison my little sister has also used these form factors and carries a 17" MacBook Pro at 6.66 lbs.
My point is that for some people this is a viable form factor.
My primary concern about the Surface Pro is cooling since it doesn't appear to have fans and the last batch of Ivy Bridge CPUs were using some questionable heat compound between the die and outer casing. I also wonder if it will be capable of delivering reasonable performance with applications such as Photoshop or run a WAMP server and IDE at the same time.
I really wonder if they can tame the heat problem in the device using current-spec chips, or they're going to stall until Intel's 2013 chips hit and they have more margin.