I need some kind of monitoring. There should be some monitoring in the new 1.4 version if I'm not mistaken but we use the Alfresco 1.3 Enterprise untill there is a stable 1.4 release.
Can I tweak the log4j file to enable some kind of monitoring? Who logs in and when, who is accessing which documents?
You could take the same approach (the aspect oriented approach) and wire in appropriate method interceptors around a few public services for now. See the 1.4 code for examples in public-services-context.xml.
There is various logging but probably not what you want.