With that pattern of use (similar to mine!) if you haven't decided already, I'd strongly recommend the 11", it's utterly sensational for just 'throwing around'!That's exactly why I think so many people are going for the machine. It's so small and compact that you can take it anywhere, farther than you would normally take a larger laptop. Going downstairs to make coffee? Take the laptop. Eating? Take the laptop. Going to a friends to watch the game? Take the laptop. Going to grab a bite to eat? Take the laptop.
I do this with my MB; can't wait to start doing it with a MBP/MBA.