I've been using it for pretty much everything the past couple days; I've barely used my regular computer. I've been writing a paper on it, which works surprisingly well. If you use it in landscape orientation the onscreen keyboard is big enough to touch type on, and I've been able to do so with abut the same speed and accuracy as on my regular keyboard. The only thing that slows me down is certain punctuation, which requires an extra step.
This thing truly is the best way to browse the web, especially for me since I don't frequent any sites that make extensive use of Flash. The iPhone is capable of viewing the full, regular Internet, but its limited screen space made it so that it was still often ideal to adapt a site specially for it. The iPad uses the same browser, outside of the UI, but the screen size makes so much of a difference. It really is basically a big iPhone, but the doubled screen size makes a huge difference.
Now that I have this, I'll give real thought to buying a desktop next time I buy a computer, or at least a larger notebook. I bought my 15" notebook for portability, but this is more than capable of doing most of the things I'd need to do away from my desk. I can't wait for OS 4.0 to make this even better, but I can already say that I in no way regret the small fortune I spent on this thing.