My gf has the 13" and it beats the crap out of my old 15" one, in terms of graphics, CPU, etc. It's a night and day difference. That being said, it's not really all that surprising, since technology advances every few months. There is a night and day difference between SSD and a 5400/7200 rpm HD. Even if it has less space, I feel like I'll get much more performance with an SSD. My LR3 library is actually on my NAS, so when I edit photos I connect via gigabit ethernet. Space is mostly an issue for me when it comes to work-related stuff, sadly. I'm leaning towards a 13" MacBook Pro with 8gb RAM and a 256gb SSD.
The more I think about it, the less the Air appeals to me, mainly because I have an iPad 2 as well and I can use that for surfing, email, etc.