Just read this and thought it worthy of a link:
Matt Gemmel talks about application design on the iPad. http://mattgemmell.com/2010/03/05/ipad-application-design
Read more for my comments:
When Gemmel talks of "in place editing" it is a techy way of talking about something that Sal Soghoian calls "point of need". It all boils down to giving the user the ability to do what he wants to do when he wants to do it. The computer can do the task the user wants to do, but the real trick is to give him the ability to do it at the right point in the workflow, with the objects that have his focused attention. Nowhere is this more important than in a touch interface.
Also I thought a bit about modes. The reason modes have gotten a bad rap in UI design goes all the way back to SmallTalk, and "no modes" was practically laid down as the law in the first Apple Human Interface Guidelines. But what is so evil about modes? It all comes down to a very common problem with modality seen all the time prior to the introduction of the first mouse manipulated interfaces. The problem? People getting trapped in software. Modes often act like trap-doors. People get in and then can't figure out how to leave. The worst examples are when the mode has a destructive and a non-destructive exit. Like a delete confirmation dialog. In Mac OS X most modes are associated with the window or the application. Still I have seen new users lost when they didn't recognize the application menu bar or the active window. Even the iPhone OS has its modes. When you switch a table into editing mode you have to choose to leave edit mode and I have seen this kind of interface confuse people. Swiping to delete is easier to learn for novices than changing the mode of the table.
So this leads to an obvious conclusion. Modes are ok as long as they don't trap or confuse the user. With a touch interface the modes end up attached to the objects of focus. And usually the obvious way out is to touch something else. So modes should be invoked by direct manipulation and also dismissed this way.
In the end my conclusion is that we will see a different kind of application emerge on the iPad, but the iPad developer can't be successful without really paying close attention to user interface design.