Maybe this answer helps:
mysql5.58 unstart server in mac os 10.6.5
I just installed MySQL 5.5.8 (mysql-5.5.8-osx10.6-x86_64.dmg) on Mac os X 10.6.5 and also had the problem that MySQL was not starting.
After reading this post: http://forums.mysql.com/read.php?11,399397,399606#msg-399606
and editing the file as suggested everything started working.
I also did
sudo chown -R root:wheel /Library/StartupItems/MySQLCOM
after reading
https://discussions.apple.com/message/12820394
since when restarting my Mac OSx 10.6.6 it kept on asking something about not enough privileges. The line above solved that issue.
Now everything is working.