Comment regards Wired's What the iPad Means for the Future of Computing:
What the iPhone did (and iPad will do) is to bring back sanity to interface design. For decades UI vendors — Microsoft, Apple, HP, Sun, etc — brought to tool/application front-end development well considered and consistent structural and visual interface elements. The tool’s new users needed only to learn how these elements were applied to the business function to use the tool. The value of this UI work was, some how, lost during the rise of the web.
The other element of the iPhone’s success is single user focus. The iPhone becomes the tool/application in use. User multi-tasking is not a requirement to productivity. Switcher was one of Apple’s greatest productivity successes. It was ahead of its time and ahead of the capabilities of the hardware. The hardware in the iPhone and the iPad make switching to another application fast and into the same context you were when you left.