I just returned from a MySQL Federal Migration Boot Camp, jointly presented by Carahsoft and Sun/MySQL. It was a half-day seminar on the topic of migrating applications to MySQL, targeted to the US Government sector. Specifically, most of the audience seemed to be running Oracle, though there were some users of other systems (Microsoft SQL Server, Sybase, Informix, etc).
Ronald Bradford presented the whole thing. I thought he did a great job giving a fair and balanced look at topics such as what types of applications are good candidates for migration, what gotchas you might encounter, etc.