Quite frankly I wouldn't like to lose the ability to handle my phone with one hand for "on the go stuff", such as maps, checking train times, etc., this is related somewhat with the size of the screen (and your hand), but also with the UI.

The N9 has been perfect for this so far, iPhone 4 is rubbish, and they are both the same size. I held a SGSII and it was "ok" (if it weren't for the UI, that is), I tried a SGSIII and I thought that was too much - walking with an umbrella in one hand and the phone in the other checking whatever you need to check is a drop risk at that size, for me at least.

Having said all this, I'd still like to have a better equivalent to the AirUI, for reading news and the like while your hands are busy eating breakfast ;-)