I am going to touch only the screen size aspect of this question. Having used a 13" white MacBook entirely for development and work (and everything else in between) for over two years, I have often found myself severely crippled by the amount of space available on my screen. Everything is fine when I am editing a single source file without needing to look at another piece of file, but when I have to reference another file or piece of documentation or a set of windows, I do feel frustrated. Often, when that happens, I feel slightly unproductive. When I do XCode development, I naturally want the XCode to maximize itself, what with the editor taking space on the right side and the project/file browser on the left. That may seem fine, and it is, but if you throw XCode developer documentation window in the mix, you start to feel a bit of frustration. And if you migrate to the world of Interface Builder development, oh dear, you will feel even more frustrated as Interface Builder is notorious for spewing countless windows all over the place (I may be exaggerating, but it indicates the level of agitation I feel at times). I am personally of the opinion that a 15" makes up for a good development machine in terms of screen real estate that it provides, at a very, very minor risk of hurting the mobility aspect of the laptop.