Research firm Create With Context’s principal researcher Bill Westerman has published an interesting account of how iPhone users learn to use their device, data which suggests the following rules for iPhone development.
1/ Take advantage of learned behaviors
“Oh, this works just like the calendar”
2/ Avoid interaction inconsistencies
“This is weird, cancel is usually over there”
3/ Provide clear conceptual link across widgets
“This button must be related to that box, they’re next to each other”