My computing habits have significantly changed since I have had the iPad and you can find it in my hands when I am relaxing on the couch watching TV, commuting daily for 2 hours, following a good hockey game, and when reading a book in bed at night. I only use my MacBook Pro now for editing video or code and for writing longer articles. The iPad serves all my consumption needs and is a joy to use on my commute where it is much lighter than a notebook.
Battery life is awesome
I have owned a LOT of mobile devices and with every single one of them I have had to be concerned and consciously think about managing the battery life. With the iPad I have yet to see a low battery warning and can go a full heavy day or two before even thinking about plugging it in.
With my smartphones and notebooks I have always experienced some kind of heat during heavy usage. This heat rise happens during charging, heavy video usage, or in the case of a first generation MacBook Pro ALL the time (to the point your lap almost gets burned). With the iPad I have not experienced ANY heat coming from it even after streaming hours of straight video content.
Apple has their new 1GHz A4 processor (manufactured by Samsung I believe) in the iPad and I have yet to experience any lag at all when running video, playing games, surfing the Internet, etc. Everything happens just about instantaneously and it is extremely refreshing to have a computing device that responds this way.
Futuristic touch experience
I know this may just be fluff and fun, but I get a real kick out of browsing and manipulating photos, working with Office documents with the iWork suite, checking out the periodic table, and using my fingers to interact with the device in ways I never have with a computer before.
I honestly think the iPad will succeed in large part due to the applications and the fact that Apple chose to use a mobile operating system rather than a desktop operating system to power the device. Also, iPhone 4G will come out in the Fall and make the device better as well.