One of my customers recently deployed intranet site on MOSS 2007. After a while we wanted to analyze the usage of this site. I was rather disappointed to see the built-in reports in MOSS. Reports are very basic and do not give you many clues about real usage of your site. You can read a little bit more in great Joel Olson post about same topic.
I just hope some vendor will provide us with something better.
Has anyone tried to implement Google Analitics on a SharePoint site? Were you satisfied with the results?