I have used a number of free services in the past. In general I have never been impressed by their web interfaces but most of them got the job done. The most recent one was StatCounter.
A couple of days ago I switched to Google Analytics (for both my regular website and this blog) because it has a really cool interface and includes a number of interesting features I want to give a try in the future. I just can't resist feeding more (personal) data to the people in Mountain View.
Why do they make these online apps so easy to use (and free)?