Last week, I had the honor of presenting at Meaghan McCann's Pay Per Click Club. Meaghan asked me to speak on Google Analytics. Her group consists of a set of people, some of whom are driving business through search marketing. All of them view the web in general as a primary sales driver.
I always pitch Google Analytics as a way to see what is happening on your site. Out of the box, it does a good job of giving a general view. The more work you put into setting up tracking goals and campaigns, the more useful your information will be. Without Google Analytics, you find yourself in the situation depicted below. You have plenty of information about how visitors are being acquired but little to no information about what they are doing once they get to your site.
The main benefit of Google Analytics in this situation is to fill in the question marks. Here's the presentation itself: