On the MySQL website can be found some articles posted under the name of: “The Twelve Days of Scaleout”, this articles talks about success stories at clients which are using MySQL services. In this articles you can find case studies on website and services like: Wikipedia (the world largest online encyclopedia), Zimbra (a leader in open source collaboration software), Alcatel (where MySQL implemented Cluster Carrier Edition database), ofcourse there are more case studies all of them are largely described on the MySQL website on the Press Releases section.