While simplicity is one of things we advocate on the blog, designing apps is not necessarily simple. To make the interface simpler, one actually has to go further with the thought at the back-end. Google's search engine interface is the simplest start page around for ages, but it's search technology is far from simple - it hasn't been bettered in a long while.
We found this nice piece at the Juice Analytics Blog, which looks at analytics apps, and how thinking through the user behaviour very carefully goes a long way. I like the fact that they recognize sites like Travelocity and Kayak as analytics apps. It's a good quick read from earlier this month.
I myself have been a fan of both Kayak and Google Analytics for a while now.