Has anyone played around with TPL DataFlows yet? It looks like it could be next step beyond using a concurrent queue for async message processing. Once a log event has had the appropriate thread specific properties evaluated it could be posted to a BroadcastBlock which would asynchronously post the message to appenders:
http://weblogs.asp.net/mjarguello/archive/2011/03/15/asynchrony-in-c-5-dataflow-async-logger-sample.aspx
