Ejdge, a netbook in the range of 400 dollars or so is capable of running all common IDEs and programming platforms. However, as they’ve already told you the keyboard is small and may annoy you. And secondly the screen or more correctly the available work area is indeed annoying. I have an ASUS 1000H (10 inch screen) which I have used for programming. My experience from the device as is (no external monitor, keyboard, only usb mouse):
Pros: Mobility, quick field testing, reference (programming ebooks etc), very handy for small algorithm development / testing (my main interest)
Cons: Small work area (Interface development is really painful), tiresome when developing / writing snipets of more than 200 - 300 lines. Keyboard is fine for me, although it’s a matter of preference really.
I had some problems with Visual Studio 2008 refusing to install, which was solved by installing through a disk image.
Personally I would go for something with a bigger screen, probably an HP Pavilion TM2-1010EA for its versatility or sth with a 13 -15 inch screen.
As for games, I don’t know if sb posted it already but in any case: Guilty Gear XX, Melty Blood, both run very well on the afforementioned netbook. Blazblue CS (the arcade hacked release) did not run. PCSX2 (PS2 emulator) is running also and I confirm Melty Blood Actress Again as playable. GG Accent Core Plus was unplayable however.
Hope this helped.