I've been using log4net for the last year but thought it would be worth trialing the Logging Application block that comes with Enterprise Library. I found this article which basically trashes it compared to log4net...but we'll see.
As usual, found a nice article by David Hayden (again) which emulates log4net's Debug, Info, Fatal type approach. He's wrapped up the types of LogEntry for each Category and is a great approach.