It would be a good idea to have "show recommended" and "show all" options on the database setup page that controlled the contents of the dialect pick-list. The list would default to the recommended set of databases we've actually tested the app against.

This would make it easier for users to tell which database choices are safe, and which are risky.

(With sufficient Javascripty goodness, you could associate tips/caveats with databases, so if the user selected the MySQL dialect the screen could display the autoReconnect=true tip, or recommend the jTDS JDBC driver for MS SQL Server, or if they selected an unsupported database, give them some advice as to what to do when it blows up. But that's possibly beyond the scope of this story)