I've been working with MySQL Master-Slave replication at work a LOT recently and one of the things that you have to do on read-only slaves is to revoke the super access to the user access the slave so it doesn't write data.

I normally setup users like this because it's easy and it gives the user all the access they need:

mysql> grant all on tasks.* to 'taskuser'@'localhost';

So when I tried to revote super I got the following error:

mysql> revoke SUPER on tasks.* from 'taskuser'@'localhost'; 
ERROR 1221 (HY000): Incorrect usage of DB GRANT and GLOBAL PRIVILEGES

The super permission can't be revoted on a specific database it has to be revoted on ALL databases:

mysql> revoke super on *.* from 'taskuser'@'localhost';

Again another hour of my life that can't be returned. :-)