My friend Ryan Turner has new blog called The Glades and has posted an interesting post about Pattern Breakages. I've worked with Ryan for about a year now and he's an experienced user researcher, a brilliant poet and an all around great guy.
Here's a quote from the post linked above. I like the idea of surprise being an incentive, but I think it's a fine fine line to walk:
Behavioral psychologists have shown that inconsistent reward is the most powerful reinforcer of behavior. So if you give a rat some cheese every time it pushes the red button and never when it pushes the blue button, it will regularly push the red button. But if you give the rat some cheese only some of the time, it will push the button more often. So being on the edge of your seat, expecting a certain outcome but with uncertainty you'll get it, brings you back for more, adds excitement and even delight.