I recently moved an application from using the Microsoft Enterprise Application logging block to log4net.
This was caused by a problem with WCF and the EAB.  There was an odd error that appeared to claim that different versions of the EAB were in use in different locations of the system (they were not!) however replacing it with the much simpler to configure log4net solved the problem. I did add a thin wrapper class so that my code is not tied to log4net.

log4net only requires that you deploy a single dll (compared to the three for EAB) and the configuartion entries are a quater the length (and don’t need a config tool to set up).