There are a bunch of different logging libraries to choose from, each with their own set of quirks and advantages. (.NET examples: log4net, System.Diagnostics.TraceSource, NLog, etc.)
The natural inclination is to abstract away those quirks and use a logging facade. (examples: Castle.Services.Logging, Common.Logging, Simple Logging Facade) That way, if a given logging framework that you're using goes stale, or a different one comes into vogue, you can just swap out the implementation and leave the code untouched.
But there are multiple logging facades to choose from. Given that the answer to many disparate logging implementations was abstraction, why not use a logging facade facade? If that sounds ridiculous, what makes it more ridiculous than the original logging facade? What makes one extra layer of abstraction on top of the logging framework the magic number?