CRM Appender currently has issues when used inside of plugins. The CRM Appender needs to be instantiated per each plugin to get the correct organization service each time. This causes an issue with duplicate log messages due to the way log4net works.
The CRM 2011 Appender is a custom appender for log4net. Instead of the basic file appender that writes log messages to a file, the CRM 2011 Appender will write log messages to your custom log entity inside your CRM 2011 organization.
The advantage of the CRM 2011 Appender is that you can view all the log messages within your CRM organization rather than a file stored on the server.
This project provides the CRM 2011 Appender dll and a sample Log entity that could be used to write your log messages to.