For me, the iPad is uncomfortably heavy at times -- especially if I try to hold it in one hand.

I mean, yes, it seems like splitting hairs -- but at some point, a device goes from being 'heavy' to 'light'. Same with thickness -- at some point a device stops feeling 'chunky' and becomes 'lithe'. I just don't know where those thresholds are :) (but I'm sure that industrial designers put a lot of thought into it).