Vous voulez faire des statistiques concernant la fréquentation de vos sites WSS, alors ce lien est pour vous :
Usage Analysis Processing in Windows SharePoint Services Sites

It is a common requirement to gather information around the Windows SharePoint site usage. Organizations prefer to find out what the popular sites in their organizations are or what external WSS sites attract the most number of visitors. This will provide information necessary for an organization to identify the important sites in their environment and properly manage them with extra resources if necessary.

Un autre lien utile si vous utilisez WSS :
Administrator's Guide for Windows SharePoint Services

Et pour les statistiques sous Sharepoint Portal, voici un autre lien :
Getting Usage Statistics on Sharepoint Portal 2003 Areas