I had an Apple Newton when it came out, and I always problems because of the size. It does not fit nicely into the hand. And it's not big enough to be a real Device that you put in front of you like a desktop or notebook.
More generally speaking: technology changes fast, but what does not change that much is the size of human hands, the resolution of human eyes, etc. And I think, from an ergonomic point of view, Nokia has done it just right. The 770 could be flatter, orlighter, but apart from that, it is just what it should be.
And the Origami (or else) is not. However, there are some cool ideas (like the semi-transparent virtual keyboard in the lower corners).