My understanding is that's not quite true. The client libraries are GPL, so you can't use them directly, but I don't see what would stop you using their ODBC/JDBC drivers with your non-GPL application (especially if you support other ODBC databases as well). The server can't be bundled in your application, but you can still get the user to install it and use it with your application.
According to the MySQL license info (
http://www.mysql.com/about/legal/licensing/commercial-license.html ):
When your application is not licensed under either the GPL-compatible Free Software License as defined by the Free Software Foundation or approved by OSI, and you intend to or you may distribute MySQL software, you must first obtain a commercial license to the MySQL product.
Typical examples of MySQL distribution include:
Selling software that includes MySQL to customers who install the software on their own machines.
Selling software that requires customers to install MySQL themselves on their own machines.
Building a hardware system that includes MySQL and selling that hardware system to customers for installation at their own locations.
It sure sounds like if your application uses MySQL and you sell your software (I presume this would include online services that charge for use of the site and that site runs MySQL under the hood), you have to buy a commercial license, and you can't get around it just by not directly distributing MySQL and having your customer install it separately.
Way off topic for PG, though, which has a great OSS license in BSD.
David