I just spent a few minutes using my old MacBook Pro (pre-retina, pre-thin), after three years of using mostly a 13" Air.
I couldn't believe how heavy it was.
I was shocked at the odd sensation that there was something spinning inside of it. It felt fragile and terrible. The hard drive actually makes different sounds depending on the angle at which you hold the computer.
The surface below the keys felt more than just warm, it was uncomfortably hot to my palms.
And the screen shocked me with how great it looked.
There's all this talk about a retina MacBook Air. I suppose that would be nice, but honestly, I'd be happy with a screen in my Air that was anywhere near as contrasty, sharp, and color-accurate as the one in that three-year-old MacBook Pro.