Here is an interview with Marissa Mayer, Google product manager.
http://www.goodexperience.com/columns/02/1015google.html
One of the answers I really liked..
Q: What is Google's secret in maintaining such a simple and clear user experience, so consistently?
A: I think Google should be like a Swiss Army knife: clean, simple, the tool you want to take everywhere. When you need a certain tool, you can pull these lovely doodads out of it and get what you want. So on Google, rather than showing you upfront that we can do all these things, we give you tips to encourage you to do things these ways. We get you to put your query in the search field, rather than have all these links up front. That's worked well for us. Like when you see a knife with all 681 functions opened up, you're terrified. That's how other sites are - you're scared to use them.

Google has that same level of complexity, but we have a simple and functional interface on it, like the Swiss Army knife closed.

Don't forget to read the full story.