Joel on Software translates the MBA "mind"-set for techies.
People who aren't programmers are just looking at the screen and seeing some pixels. And if the pixels look like they make up a program which does something, they think "oh, gosh, how much harder could it be to make it actually work?"
The big risk here is that if you mock up the UI first, presumably so you can get some conversations going with the customer, then everybody's going to think you're almost done. And then when you spend the next year working "under the covers," so to speak, nobody will really see what you're doing and they'll think it's nothing