David Coveney from interconnectit.com has written an excellent tutorial of how to use MySQL Workbench with XAMPP, a very nice bundle of Apache, MySQL, PHP and Perl. If you are running XAMPP or what to give it a try, make sure to check out his tutorial that describes how to set the correct MySQL Server Instance profile parameters.
This tutorial is also a good resource for people who do not use a default installation of MySQL and need to manually adjust their MySQL Server Instance profile parameters in order to make their setup work with MySQL Workbench. Default installations should work out of the box of course.
Please find the tutorial here: http://www.interconnectit.com/764/using-mysql-workbench-with-xampp/