While reading Derren Brown’s book 'Tricks of the Mind' (thanks Simon) I began to see some overlap between performing close-up magic and designing user interfaces; it comes down to understanding and predicting your audience’s attention.
The approach however is from opposite sides of the problem; while the interface designer tries to focus the attention of the user to enable them to achieve a task, the magician relies on our inability to focus on everything to perform their trick. Especially when we are concentrating on something we can easily miss even the most obvious things, so while we are looking to see how the trick is done it distracts us from how it is actually done.
Try this awareness test:
It makes it clear that if there is a lot going on then not only is it harder to find the information you want, but you can miss important information you didn’t know you needed. In the context of interface design it can be frustrating for a user and ultimately may prevent them from being able to achieve their goal.
We also learn not to see things through experience and expectation. An example of this I saw recently was putting a quick link to an F.A.Q. page in an area of a page normally reserved for advertising, as a result few users saw the the new link; we have become conditioned to expect advertising and therefore don't look at that area of the page. See Nielsen's research on this banner blindness.
As interface designers we need to consider that to break with expectation can mean we create something that can stand out, because it breaks from the it's surroundings conventions, however it might never get seen, such as when we put important navigation elements where we expect to see advertising. So we need to understand when it's appropriate to use the audience's own expectations to help them find the information they need.
Keep it simple
When dealing with an audience's attention it helps to remove distractions. Keeping an interface as simple as possible and removing unnecessary distractions, can help make it clearer and easier for the user to focus. But it's important to not throw out the baby with the bathwater, if you remove too much information then there aren't enough cues to know what to do next.
One time performance
This is important if it is an application that is used rarely or as a single experience. The reason you will rarely see a magician repeat the same trick is because it gives the audience the opportunity to see it in a different way, we know what is coming and we've already studied the trick once, if we see it again it makes it easier with each consecutive performance to see how the trick is achieved. This is the same for interface design if we know what to expect, through repeat use, it is easier for us to know what to do over time as we can handle more information and learn the interface. In which case we can adopt more complex interfaces, that offer more functionality, but take longer to learn.
In conclusion we need to understand that our awareness and attention are often compromised and easily distracted, and take this into consideration when designing user interfaces. A good experience is like a magic trick, we might not be aware of exactly how we got there, it seems easy, but we are delighted we did.