Just a quick tip on monitoring the queries that mysql is handling on a production site. You can use the mysqladmin tool to return a list of the processes currently being handled. Combining this with the UNIX watch command allows a real-time monitoring of what's going on.
watch -n 1 mysqladmin processlist
The -n 1 specifies that mysqladmin executes every second. Depending on your set-up, you may need to specify a mysql user and password:
watch -n 1 mysqladmin --user=<user> --password=<password> processlist