I am using the RollingFileAppender and the Size rollingStyle. By default it creates backup files with a numbered extension, this drives me nuts. Is it possible
The PreserveLogFileNameExtension property set to true should do the trick. Note: this property is not available in the currently released version 1.2.10 but is part of the current source. If you grab and build the source you're good to go.
Update: it is great to see log4net is moving forward. Version 1.2.11, and with it the PreserveLogFileNameExtension property, have been released.