Before a Magento site goes live, we need to create a cron to keep the log files from growing too big. Magento comes with a script thats in /shell/log.php that will do the job.
Set it for once a week or so around midnight.
/usr/bin/php /path/to/site/shell/log.php clean –days 30
Another think you should do is disable some of the logging in the first place. I posted that a while ago.