On the whole bed/couch question...In bed, I don't notice much of a change coming from my iPad 2, other than the bigger screen of course. It just needs to be propped up on a pillow or whatever. The couch is where I notice a big difference, I really like the larger screen resting on my lap. The larger size is more comfortable and viewing size and distance matches well.
Jury is still out for me though, but I'm leaning toward keeping the 12.9"
Side note: The one negative comment I will make is that this could really benefit from a stand, a la the Surface. I know that isn't feasible, but I really want to prop this thing up with something other than my hand or pillow. Also, this thing screams out for a pro-ified iOS.