impersonation
<system.web>
<identity impersonate="true" />
</system.web>
Configuring log4net for SharePoint Windows Authentication
http://mikeknowles.com/blog/2009/02/17/ConfiguringLog4netForSharePointWindowsAuthentication.aspx
log4net does not work in IIS
http://forums.asp.net/p/1420781/3153374.aspx
http://stackoverflow.com/questions/1061857/sharepoint-and-identity-impersonatefalse