I have been doing so for about 6 years. In my experience, gaining screen real estate is amazing at first, and losing it really hurts at first, but in the long run, it doesn't make much difference.
My 13" Macbook Air serves me well as my primary development and design workstation. For purely development, I would love to use an 11" Air, but Photoshop is a bit too cramped on it.
My 27" display gets used for watching movies mostly these days. I do go through phases though, and will probably try using the large screen for work again eventually. For now, I find the smaller screen less distracting.
I do it on 12". Absolutely no need for any more for development, not even one bit.
Now, design work obviously needs a lot more, but that's offset by the fact that my HP 2730p is also a tablet with stylus, which made me extremely productive in dishing out graphics.
My laptop is in for repair and is taking a disturbingly long time, but my friend lent me his out-of-use EeePC with a 10" inch screen.
I'm amazed at how much work I have actually managed to get done. When I'm in the office I dock it to a keyboard/mouse/monitor, but even on the road I've found myself able to use it, once I adjusted to the keyboard.
If you run light-weight ubuntu (lubuntu for me), have your browser/editor/terminal in fullscreen, and you can get back to work. The slow processor does struggle with our companies rails app though...
Yep. I've had 13in and 15in MBPs but I prefer my 13in MBA. Work gives me the option to get a 24 in monitor for my desk but I haven't bothered to request one.
