What is the best practice for formatting logs?

I like this format for log files:

$ python simple_logging_module.py
2005-03-19 15:10:26,618 - simple_example - DEBUG - debug message
2005-03-19 15:10:26,620 - simple_example - INFO - info message
2005-03-19 15:10:26,695 - simple_example - WARNING - warn message
2005-03-19 15:10:26,697 - simple_example - ERROR - error message
2005-03-19 15:10:26,773 - simple_example - CRITICAL - critical message

This is from python’s logging module.
I usually have a file per day, one folder for each month, one folder for each year. You’ll get huge log files that you can’t edit properly otherwise.

logs/
  2009/
    January/
     01012009.log
     02012009.log
     ...
    February/
     ...
  2008/
   ...