We got a king size after we....uh.....broke our queen size mattress. Since we had to do modifications to the queen size box spring to get it up the stairs we opted for a two-piece king size mattress, which fit up there with no problem. These days we do wake up fairly far apart on the thing, but I use a big pile of pillows to sleep in a semi upright position, so it makes it awkward sometimes to sleep close together. Usually we do the spoon thing for a while before one of us drops off to sleep.
I really prefer it to the early days in which we both had twin beds.