This is interesting: Facebook wrote their own logging system [1] instead of using syslog. Their system only has two pieces of informtion—a catagory and the message. No facilities, no priorities or levels. I think in Facebook's case, they log everything so there's no need for individual priorities or levels [2] (the argument here is: you're going to log everything eventually anyway, so simplify the process).
Another note: when your configuration file is too complex [3] (or in other words—an ad-hoc declarative language [4]) perhaps it's time to give up and just use a scripting language for configuration (I skipped straight to using a scripting language for configuration/logic).
[1] http://www.facebook.com/note.php?note_id=32008268919
[2] http://highscalability.com/log-everything-all-time
[3] http://blog.gerhards.net/2009/12/rsyslog-feature-schedule.html