I hardly ever use the classes in the System.Diagnostics namespace.  As much as I’d like everyone to believe that it’s because I’m such a rockstar that I don’t need them, it’s really just that I generally use other techniques.  With Visual Studio providing so many tools for debugging I’ve rarely had reason to dig into this namespace much.  Sure, I’ve used the Debug, Trace, and EventLog classes but I haven’t taken the time to investigate what else is in there.