I've been a user of the Apple iPad since August 2010.
Originally, my thought was that I would use the device as a experiment to see how it might affect my productivity and where I could find it helpful and useful. Also, I broke my #1 rule about new technology - never buy the first rev of anything. I bought the first rev of the iPad only six months after its initial release, and before the second release of the product.
Why was this worth an exception to the rule? All the reviews I'd read reflected on software flaws - no printing capability (now available as iOS 4.2), limitations of the common productivity apps - Numbers, Pages, Keynote, to name two - which were all about software. Software can be updated and the missing features delivered in updates, which as history has shown was totally 100% accurate prediction of the future.
Also, it occurred to me, that unlike the original Mac, the iPad's OS is the iPhone's OS and apps and sync software (iTunes) are well understood and entrenched in millions of users experiences and routines. The power of the App Store will only ensure that the iPad software market grows quickly with apps optimized for the larger screen.
Part of the reason I had the rule was because the first rev is always too experimental and too expensive - battery problems need to get fixed, electric doors (on minivans) need some tweeking to work more reliably - and I didn't want to pay extra to be a guinea pig.
Positively. I use my laptop less and use my iPhone less too. The iPhone is now just a phone, while the iPad has taken on most if not all of the non-phone functions that I used to rely on the iPhone for - calculator, music player during treadmill exercising, note taker, appointment calendar, minlet complement. Probably the most useful to me is the level of synchronization across my iPad, iPhone and Mac assures that no contact is lost, no email unread and no appointment is missed.
As well, my handwritten notebook, a moleskin (about $10 at Barnes and Nobles) is barely used anymore.