Just found this one entertaining, so I thought I'd share; from the mysql manual at http://dev.mysql.com/doc/refman/5.0/en/create-table.html:

For other storage engines, MySQL Server parses the FOREIGN KEY and REFERENCES syntax in CREATE TABLE statements, but without further action being taken. The CHECK clause is parsed but ignored by all storage engines.

In other words....the FOREIGN KEY, REFERENCES, and CHECK in a create table statement don't actually do anything.