I've been watching the folks at The Writer's Block struggle with a user interface problem for at least the last year: how to get people to use the half of the door that works and not push open the broken one. After putting up signs that customers didn't read (ironic for a bookstore) and graphics that people ignored (I thought the big arrow pointing to the other door would work), they've resorted to putting a trashcan in front of the door.

I can think of several design lessons that could be gleaned from this, but the main one I'd go with: the practical solution isn't always the prettiest;