From my personal experience, I liked coding Python with Textmate on a MBA, but not Objective-C with Xcode. Py/Text didn't take up much space and was easy to work with. Obj-C/Xcode demand lots of real-estate space, so the tiny screen was a hinderance.
So I'd advise that if you have a language that's 'tiny' and a minimalist editor, you'll probably do fine on a MBA. If the language and editor take up lots of space, I'd stay away and go with something that has a bigger screen (exception if you plan on using an external monitor).