Xshift-- I've taken my iPad with me all over, but I hardly ever find myself trying to work with it outside. There probably would be some squinting involved there, but I'm not sure.
When looking through the available apps for working with pdfs on it I was very concerned about the question of speed you raise. I wound up trying a couple of different apps before settling on the one I currently use; I was led to try this app because user feedback had pointed out that it handles oversized pdfs really well, and I couldn't agree more. If you are in Germany (Weimar), for instance, and you want to go to Zimbabwe, it literally takes half a second to get there (the app gives you the country index as an easily navigable menu). My usual consultation pages are bookmarked, which gets me there even faster. It would take me longer to find the page if I had the hard copy in my hands. And of course you can zoom in and out of pages with two fingers, as you would on your ipod/touch/iphone. The one thing that can be a bit slow is searching, but that may be more due to the fact that you're looking for a word or two in 2250 pages of searchable text... (Krause 1901-2000 cat).
The thing I've become most excited about lately is the VGA output cable they sell for it, which will allow me to use it for many work-related tasks.