iPad apps and websites designed for iPads are better than they were last year, however there are a few design issues which keep cropping up.
Some of the design issues stem from the fact that the iPad user 'taps' the screen, rather than rolling over items with the mouse. This means that they miss the cues which would identify an item as 'clickable', unless the cues are visible at all times.
Another issue to do with the touchscreen is that the user touches the screen to scroll, and often something interactive is touched in the process, sending the user away to a new page. Including 'Back' buttons to take the user quickly back to where they were is helpful. It can also help to add a 'more' button, so that scroling can be concentrated in one place.
Another important consideration is screen real estate - it's important not to waste space, and to make clickable areas large enough to see and touch. There is also a new acronym - TMN - Too much navigation.
The report has many examples, and also a summary of how the iPad is used now. One finding is that at this point in time most iPads are shared.
You can download the 2010 and the 2011 iPad Usability Reports free of charge at the Neilsen Norman Group website.