That was my point: you wouldn't on a MBA like computer. You would on a high-performance small formfactor laptop like the x220. See my other replies for more information
No, you'd do it on a Mac Pro, or, if you want to try and save money, on a PC hidden in a closet somewhere. You'll need a PC hidden in a closet somewhere as soon as you need a cluster anyway. Same for compilation, Xcode even makes it easier for you to set up a distributed build.
Now, there are reasons to get a strong laptop. A good one is if you need some serious power on the go. Are you running that bioinformatics software while on an airplane?
No, you'd use EC2 servers to avoid doing your own maintenance, and you'd do so as a last resort because GUIs are useful and remote development is laggy. http://www.useit.com/papers/responsetime.html
