I was reminded this morning that user interfaces aren't just about being pretty or looking good. They're about putting the right information in front of the user at the right time. Good user interfaces are also about helping users understand the meaning of that information in context: How has it changed? Is this a normal value or not?
Bad user interfaces can and do lead to disasters. If you're lucky, your user interface is to a web site and the disaster is that you lose users. If you're unlucky, your user interface is to some life-critical piece of equipment and someone dies. (Don't roll your eyes, it's happened.)
One of the more famous user interface disasters is Air Inter Flight 148, which crashed in 1992. Why? Bad user interface played a part. The pilots thought they were entering a rate of descent and they were actually entering vertical speed; 3.3 degrees down became 3300 feet down. That's an important distinction when a mountain is in your path. The problem was a bad user interface; it didn't show the pilots what they had actually entered, and they didn't figure it out until it was too late.
It's easy to talk about the user interface as the "making it pretty" step. And user interfaces can be pretty. They also need to be functional. Aim beyond "has all the data" and shoot for "conveys information". You users will thank you for it, even if no one dies.