A short while ago, I did a presentation for the Twin Cities .NET user group on log4net. (You might recall an earlier blog entry where I discussed using log4net with BizTalk 2004...)
The presentation was not specific to BizTalk 2004 - instead, it attempts to describe why I think the log4net library is so very well thought out. You can grab it here, if you like.
The last slide references Loren Halvorsen's comparison of log4net and the new Microsoft Enterprise Library Logging Block, which I would recommend taking a look at (the comparison, that is.) Tom Hollander (among many others!) later weighed in with this piece.
Lastly, 1.2.9 beta of log4net has recently become available (release notes here)....However, my extensions to log4net have not yet been updated to reflect this new drop. I'll be sure to post when I'm able to update.