Stupid question time: Why actually develop software that does this, instead of just analyzing the logs? Seems a bit redundant if you ask me.
The client wanted to see live users online. This can plug into any website regardless of log format. etc etc etc.
The main goal of the task (set by a client) was to be able to track what users do when they visit from a predetermined source.
That link you visited could be put in a newsletter sent out via email. The client sets up a "group" in the tracker script. That group then lets the client input any web address and spits out a link which will trigger the tracker correctly. Then they mass mail their link and see how many people come back to the site and where they visit on the site during that session.
Very important if your trying to market something to see if they are getting to where you want them to go, and what other trends arise.
Make any sense ?
For example, I could leave the tracker going for a week. See which pages are visited most and then go to those pages and tweak the layout or make some changes. See if then after that the average time spent on the site increases.