I checked it out assuming it is extremetracking.com. I have some free tracking provided by my host that is similar to what they provide. The unique things about opentracker are the ability to see when people are on your site in real time, and more importantly, seeing a “clickstream” of which pages they went to in what order, and how long they stayed on that page. If I see people going to a certain page, but never staying for more than 10 seconds, then I know I need to work on that page with either more content or a better heading to catch their attention.
Again, I am not sure this is worth the 19.99 a month or whatever they charge, but as a new webmaster, I am fascinated by it. I could see how when you get 1K uniques a day the aggregate reporting is more useful.
CBW