If you ask around about shared hosting setups with MySQL everybody is frightened. In fact it looks like shared hosting is one of the most difficult setups you can get.
The number of users is big, the number of tables huge and the load pattern is completely unpredictable and the queries often very, let us say: non-optimal.
Here one of the DBA wisdoms come into play: Controlling developers is like herding cats.
If you talk to the Shared MySQL Hoster they confirm that this setups are very demanding!