I have an iPad, and it's great for most of the things you mention, but extended typing on it can get a little tiring.
The iPad isn't quite a "mobile computer", IMO. It is limited in that regard to what you can easily install/run on it. And I don't mean that as any kind of anti-appstore comment. I just mean than if you want to download, unzip, and hack around with with template or script you can't do that directly on the iPad. Not sure how you operate, but I've been using linux and now OS X laptops for the last ~10 years. I like being able to test some things locally on my development machine.
A netbook is most likely a better choice for what you want to accomplish. A physical keyboard makes writing long documents trivial, and you get access to a terminal for your web development.
The iPad was made for recreational use, basically for 'having fun', playing games, going on Facebook, ect.
I used to run around with an iPad. But now I have the 11" MBA in my little Crumpler bag. And I can do so much more than on the iPad .. Love it.