I went through a 2010 13" Air and then a 2011 11" Air before finally end up with a 2011 mbp 13" (the I7 version). The 13" Air battery was the best I had ever seen but the MBP I have now easily is getting 45 minutes to an hour more. I've been writing and surfing for just under an hour and have 90% left right now.
The screen quality if exceptional. Far better than the Airs. The Airs have funky colors. They are sharp and have good contrast but they fall all apart in the color quality and gamut aspects.
The machine is fast, very very fast. The hard drive is slow though. I'm going to replace it with a SSD in a month or two. The size is perfect as you can do desktop related tasks without hassle and yet grab it and take it on the road very easily. Almost as easily as the Air. The Air may be the ultimate travel laptop but the mbp 13" is very close and you just get more. One thing you get is you don't need a lot of dongles and I think having less crap hanging off the laptop is a great equalizing argument in relation to the weight difference argument.
I find the longer travel of the keyboard on the mbp is less fatiguing to my hands as well.
Did I mention that photos look amazing on the mbp and lackluster on the Air? Yeah, I did, but it bears repeating. DON'T get an air if photo color quality matters in your work or play.
What is really cool about the mbp is that you really feel like you are using a mbp 17 ultimate that went through a shrinking machine. You really feel like you have a shrunken version of that beauty which is something you never really feel with the Air.
Now, I think the Air will improve in upcoming revisions and outshine the pro most likely in more ways but until they get that screen upgraded I'm just not going to be interested. I think they are working on a better Air screen, I've seen rumors.