Upgraded from 11" MBA to a 13" rMBP. Next upgrade will most likely be a 15" rMBP, or what ever it is called in 3 or 4 more years when I upgrade again.
At home the 13" is great as a living room surfer. This is my personal laptop, but I occasionally use it for work. And when I take it to work, I wish I had the larger screen.
I am 6'3" and 240 lb, so the extra weight for the 15" would not even be noticed in my backpack.