I spent the last week carrying my iPad with me to meetings and using it as my main system at home an in my cube. My laptop was used for a few things, like the performance monitoring tool AppDynamics - which needs a bigger screen and is flash based, but just about everything else was usable on the iPad.
I have the apple case, which I think is essential, as it holds the iPad up at the right angle to use on a desk or lap, as well as protecting it and making it less slippery to carry around. I got the Video out cable but haven't had a chance to use it yet. After intensive use, the battery is still at 60% or more each evening.
I like the speed at which apps like mail and calendar come up, and they are both very nice to use, I prefer them to entourage on my Mac laptop. I spend a lot of my day reading writing and deleting email. Safari is also fast and worked well for gmail. I imported a PowerPoint presentation to keynote on the iPad and it needed adjustments to font sizes in diagrams, and lost some color coding, but seems like a usable tool. I will switch to keynote on my Mac as well and hopefully it will be compatible.
I have a VNC app, but moving the mouse cursor around is a a pain so it's only useful for emergency access to my laptop.
The other app I use a lot is NewsRack, which tracks about 100 random rss feeds for me by keeping in sync with google reader. I get most of my news and keep up with friends blogs this way. Compared to the iPhone version it seems to update much faster and the extra screen space is well used. The BBC app provides a more visual way to track stories, and the Guardian Eyewitness photography app contains stunning images, it's one of the most popular free apps at the moment.
Typing on the iPad is better than expected with two caveats. I keep hitting the b or n keys when I mean to hitbspace (like that), and the auto correction system is a bit over-active so I have to proofread what I write more than usual.
Of course I have been watching movies with the Netflix app, and have used the eBay and Pandora iPad apps, which look good. I'm still using the iPhone version of echofon as my Twitter reader, but I will try out the official twitter app when it comes out.