I was setting up Genius in Itunes tonight and I got to the form below, and didnt fill out the second input because it looked like they wanted AOL credentials. Then, when the error came up, the red arrow and the blue triangle point to the same place, kind of confusing.
Now, I know that if I would have just paid more attention, I would have gotten this from the start. Even so, I sometimes stop paying attention and hope that the interface will be intuitive enough that I can just use it without thinking. I know, lame right? Not necessarily, I have found that this is a good way to test out user functionality.
If you have to stop and think about how to make the interface work, then there is something wrong. The idea is that you want the users who pay full attention to find things that are especially for them, and for the other users you want them to be able skate by.