I was looking for a way to NOT startup MySQL on my Ubuntu machine, while booting the system.
In previous versions, this could be easily done with the rcconf tool. I'm using Ubuntu 10.04 (LTS - Lucid) now. But this was the result with rcconf in Ubuntu Lucid (10.04 LTS):

So MySQL was starting up, every time at boot time, but the rcconf tool was telling me : "hey, MySQL doesn't start up at boot time!".
After Googling a while, I found out that MySQL is now starting up by upstart (http://upstart.ubuntu.com/). In order to disable MySQL, execute following steps:
<a href="mailto:jochen@DESKTOP">jochen@DESKTOP</a>-JOCHEN ~ $ sudo nano /etc/init/mysql.conf
Now comment the lines marked with "<-------"
# MySQL Service
description "MySQL Server"
author "Mario Limonciello "
# start on (net-device-up <-------
# and local-filesystems) <-------
Reboot your system to test :-) !
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