I ended up going with an Asus Eee Pc Seashell netbook, which cost about $250. It has a great battery life (at least 6-8 hours of active use) and is small and light enough that I think nothing of toting it back and forth to the hospital every day.
However, I don't actually use it that often for discharges or looking things up -- now that I have an iPhone, I find it MUCH more convenient for quick web searches, and while the netbook is portable, it's a pain to lug it around all day and it doesn't really fit in my white coat pocket. Sometimes I take notes on it during didactic rounds. And our hospital has about 20 computers for about 80 rotating students, so it saved my butt on many early mornings when my SOAP was due and I couldn't find a free computer anywhere!
But I could have done all of those things on an iPad, too. And I don't think any of it (well, maybe the SOAPs) was mission critical. I think iPads are definitely better for organizing electronic resources, and my friends who've downloaded electronic textbooks onto their iPad LOVE LOVE LOVE them!!! Those types of documents are a pain to navigate on the netbook.
I guess if money wasn't an issue, I'd go with an iPad. More versatile, lighter, more user-friendly. But the netbook was fine.