I was fortunate enough be given an iPad through work. It was easy to justify based on what I do for a living. The reality was that I was prepared to buy one for myself, so I am sitting on the money to do just that at a later date.
-We haven't seen a significant change in how we interact with computers since the keyboard and mouse (a late 1960's invention). We can point to tablet PC's as the early innovators, but ultimately that isn't true. They did feature pointing devices and a flat screen, but the operating system and user interface was pretty much the same interface that was designed for a keyboard and mouse. There was little or no attempt to rethink how something would work without a physical keyboard. Like many things Apple, the iPhone/iPad is not as revolutionary as profoundly evolutionary. With the iPad developers now have a successful model for how a touch interface can work on a tablet. This is good for everyone.
-The iPad represents the shift from computer platform to computing appliance. There are many examples of this now, but the iPad represents the most blatant. The Tivo is a computing appliance in that it runs an operating system, has a processor, ram and storage, and a modest amount of 3rd party support. However, unlike a personal computer, it is a "closed" environment that not just anyone can write for. Videogame systems, to some extent, represent the same idea. It is possible to hack these to run 3rd party applications, but it's really not the intended use. The iPad represents a further shift in this idea, whether someone agrees with it or not.
-There are notable gaps in the experience. Flash is the most hotly contested. It is a disservice to not support embedded flash applications in the browser. There are legitimate technical reasons to exclude flash, but at the end of the day I would have included Flash application support in the browser, but not necessarily for stand-alone apps. As for flash as a video player - I think that bird has flown. The HTML video tag has too many benefits to not adopt it. The "which format" issue will sort itself out - I root for the open source alternatives - but the pragmatist in me says that h264 will win - hardware acceleration, better tools, more content.
-Battery life on the device is a game-changer. I am watching my battery go down on my macbook right no, but on the iPad I am forgetting to check because the battery life is so phenomenal. It will be a deciding factor for some as they consider buying a tablet.
-Some applications really shine on the device. My music apps (such as megasynth, bebot etc) work fantastically on the iPad - megasynth has become something that is actually more than just a novelty - truly useful. I can't see what midi support for it could be like. I am running these in pixel doubled mode, but the double size make it more useful. I look forward to seeing what kinds of graphic applications show up on the device.
It will take about a year before the other manufacturers begin to ship truly competitive products to the iPad. HP's purchase of Palm (and WebOS) has some attraction. Most of the tablets out now are using hardware that is not nearly as power efficient - just netbooks in a different form factor. Price will be a factor - but just like is the case with netbooks - there is definitely a price/peformance tipping point. The $150 netbooks aren't selling because they are too underpowered for what people want them for. A $200 tablet versus a $350 tablet may be a world of difference. Apple figured this out.