glog implements log levels with a nice boolean alias. Starting at line #983, the Verbose, when wrapping the boolean true causes its various functions to invoke the logger. So if you pass in -v 3 on the command line and use glog.V(2).Info("hello") in code, your logger will write the message. This allows glog to have far fewer log levels than most loggers. It's still a log more complicated than the build in log, which is a minimal stdout/stderr logger.

My levels are -v 1 to see high-level success, -v 2 to trace activity, and -v 3 to dump object values. I also log user-level and processing failures as Warning, and critical missing functionality as Error. I haven't found many uses for Fatal or Exit logs, yet.