I like the iPad touchscreen a lot (and the one on IA Writer app even more so) - I find it easy to use and able to type at a decent speed. However, if I'm away from home and going to be typing for extended periods, then an external is the way to go.
Re: netbooks. Well, firstly the iPad gives me a different experience to a netbook and with more than a few apps I like (e.g. Moot Filtatron) afford me greater creative opportunities. Also, and very importantly, I find netbook keyboards to be on the cramped side (however, I like Samsung NC series as they tend to be larger than most) and find it hard to touch type.