I do development with a maxed out 2011 11" MacBook Air. It's tiny, just bigger than an iPad but has a 1.8 GHz i7, 256 GB SSD and 4 GB which has been adequate.

I do development with a maxed out 2011 11" MacBook Air. It's tiny, just bigger than an iPad but has a 1.8 GHz i7, 256 GB SSD and 4 GB which has been adequate. The screen is small but I don't do much development where I don't have a large external monitor. In my home office I use a pricey Thunderbolt Display which gives very good docking capabilities with a simple connection. I love the nearly invisible weight and very portable size. Highly recommended if your responsibilities don't require massive hardware capabilities.