I just finished reading the Log4Net Introduction and FAQ and realize I've been missing out all these years. I won't retrofit my current App (just yet), but I definitely need to give Log4Net a try with future projects.
In particular, I like the hierarchical logging that it enables, both with log levels and with the equivalent of logging namespaces. For exampl, you can create a log named "Security" and another log with "Security.Access". If you set a log level on Security, the Security.Access will inherit that log level (unless you also specify a log level for it). Very cool.