iPad Usability:
http://www.nngroup.com/reports/mobile/ipad/ipad-usability_2nd-edition.pdf
This article attempts to do an extensive study of the user experience with the iPad. It is a one-year followup to their first study, just to see how things have changed in the product's infancy. The overview startlingly resembles my own user experience. Read-tap asymmetry is a problem with many different websites, and the solution of zooming in to tap, or zooming in and scrolling around through a list is somewhat annoying. Websites with substantial interaction, such as Safari Books Online, are a chore to deal with, especially when they're as poorly laid out as that site is (a book's section traversal is always down at the end of the section you are reading at the time, so it takes a lot of scrolling). Accidental activation is really annoying, whether you are trying to click elsewhere, or trying to scroll. The only time I've clicked on an advertisement in the past year has been with an accidental click. Typing on the touchscreen is somewhat annoying, since it's usually a slow, two-fingered ordeal. In my opinion, it's the one thing keeping iPads from completely wiping out netbooks. The note that iPads are mainly used for gaming and media consumption, rather than productivity matches my own experience as well. It seems likely that if a few of the problems mentioned in this article are fixed, or mitigated, the device will make for a better productivity experience.
Of some note, I was not able to get to the other two articles, unfortunately. The ACM site apparently wanted me to pay for the articles.