Would never program on a netbook even if you paid me and gave me a decent keyboard and widescreen external lcd. Might as well take the money and buy a desktop.
@Gezza: Basically get anything with a decent processor, fast memory and as big a screen as you can afford with a high resolution. If you're not looking for too much portability and don't mind shifting a heavy machine around, go for 17" and possibly 7200rpm hard drive. Also would recommend test driving the keyboard before but buying online makes that difficult