Mac dilemma

Guys, I'm switching to a Mac, mainly because I want to develop apps but I'm rather confused about which one to buy. Will Xcode 4 be able to run properly on MBA 13" 4GB RAM 128 GB 1.8GHz ($1199) ? I want to go for the Air because I just love its design and thinness but I also want proper functionality. The other option is MBP 13" 4GB RAM 500GB 2.5GHz i5 (also $1199)

I know that the MBP seems like the obvious winner but the thinness of MBA wins me over.
Please share your views!