There is also the ident string that is prepended to every message. Some syslog daemon can filter on that.

The huge advantage of syslog is that it is standard interface. People can configure logging without worrying about special. The other big advantage is that it does privledge separation and synchronization for logs. Two processes can write to the same log files without worrying about locking or synchronization. A process does not need to have permission to write to the log file since it is isolated by the syslog daemon. Akso, syslog has builtin facilities for remote logging.

I have heard good things about Log4Perl as a general framework.