I've been discussing Monolog in Drupal events (DrupalCamp Lyon, DevDays Barcelona) as a possible alternative to the legacy Drupal
watchdog() service for quite some time, but never took the time to explain it in writing, and the feature freeze date is looming ahead, so since I'm taking part in th Gent code sprint, and code has been starting to take shape
here is an overview of the Monolog classes.
The diagram below is a simplified version of the Monolog architecture. It includes all classes and interfaces, but only the most significant methods, no constants, and none of the non-bundled classes and interfaces upon which some of the builtins depend.