I tried a netbook a coupla years ago. It was a nice toy, but I found it to be unusable for anything beyond the trivial. The keyboard was just a little bit too cramped for me to comfortably use it, and the screen way too small. The screen was so small that I couldn't really have more than two files open at once in my editor, whereas my typical working environment, even for working on my own personal projects, will have at least four or five files open at once, all visible at the same time, plus a terminal running tests, plus a terminal showing a log file. One 28" and one 17" screen is barely enough!
After not using the machine much for a few months, I gave it to a friend who uses it as a web and email terminal and loves it. Maybe I'll try a netbook again some time, but I don't think it's very likely. I just don't see any benefits over a full size laptop, other than the price, and for me price is far less important than functionality.