The surprising ambiguity of icons
Create with Context’s recent slideshow “How people really use the iPhone” reveals among other things how difficult it can be to intuit actions with confidence by icon alone. The slideshow notes that test subjects using Mobile Safari for the first time made some reasonable but wrong guesses about what several of the icons meant:
- They thought the magnifying glass
to the left of the Address Bar meant “zoom this page”.
- They thought the Plus icon
at the bottom of the Mobile Safari screen meant “increase the font size”.
- They thought the Book icon
meant “read this page”.
These are perfectly reasonable interpretations of those icons. There are examples in Mac OS X as well. For instance, in Safari it’s not immediately clear that the 
icon means “reload the current page”. You learn that this is so, but users might also initially believe it means “rotate the window to the right” or “rewind/go back”.
Fortunately, icons with multiple possible interpretations usually make more sense one way than another, and so long as the associated action is not destructive, there’s little harm done if the user is initially surprised. Safari’s icon seems unlikely to mean “rotate the window to the right”, so it probably means “reload the page” and possibly means “rewind/go back”. But even when an icon might not represent an action as clearly as you think it does, once you click the icon the relationship between icon and action usually becomes clear.