Metaphor is seductive. It’s an easy shorthand to explain things that have never existed before (such as the desktop model). It’s almost impossible to avoid for an interface designer when translating something that previously existed in the real world online. But it hinders. It encourages bad icons. It creates limited or inaccurate expectations for the behavior of the interface.
(the first time I used a Mac after years of PC use, I couldn’t figure out how to get the CD-ROM out of the CD drive. Someone said “Drag the CD icon into the trash can.” I said “You’ve got to be kidding”)
Of course metaphor can be used positivly, to aid understanding. But there is so much bad metaphor out there. Sure the southwest airline ticket booth is gone, but Denny’s lives on. Look at the top 20 websites, and ask yourself, how many of these base their interaction design on metaphor? And then next time you design a site, ask yourself, can I do this without a metaphor? Can I just make the thing the thing?
Do Metaphors Make Web Browsers Easier to Use? has a potential answer, recommending “composite metaphors” to marry the ease-of-comprehension of the metaphor with the extensibility of none.