Every single thing on the screen is something the user must look at, understand, and decide if they should ignore.
The biggest pitfall of programming, especially web programming, is how easy it is to add more features. Pretty soon the entire screen fills up with buttons, widgets, and other distracting paraphernalia. And you can’t remove any of it.
Maybe someone wants to see your Technorati score, or how many subscribers your blog has, or what the weather is in Scandinavia. For everyone of these widgets there is someone who wants to see it and 1,000 people who don’t. Trying to make everyone happy leads to cluttered UI that nobody likes.
You can save yourself from clutter with focus. Don’t try to do 1,000 things moderately well, do one or two things really well. Maintain a laser-like focus on serving most of your users.
A popular tool for focused UI is a mission statement. Answer the question, what does this UI do? Jason Zimdars answered that question very well. He is the newest designer at 37 Signals. As a web designer you might expect his site would be full of bells and whistles, but he chose to forgo the clutter and answer a simple question: who is Jason Zimdars?
He could have put a lot more into his page, but it would have diluted the message. Instead he focused on two simple topics and made sure they were presented well. The web already has too much clutter. Jason’s site stands out as much for what it is as what it isn’t. Your UI can do the same.