I was wondering what data about your users/visitors gives you most value? Do you track on every page, or only landing page / signup page? And what tools are you using?
Google analytics is great. Depending on the project, I will often settle with its features (which can be pretty extensive) and just track url hits and traffic sources.
The only problem with Google is you can't directly identify any user, its all aggregate anonymous data. I have also written some code for when I don't want my info to be minimal. On sites where I want really in-depth information, I use a tracker that logs in-page activity, user behaviour, etc. on top of GA. :)