Exchange Data Store Change Still in the Cards: "While Exchange 2007, the upcoming e-mail, calendaring and messaging server from Microsoft, is still based on the Extensible Storage Engine, a derivative of the Jet database store, the company says it remains committed to unifying this with the SQL Server database store going forward.
They just don't know exactly when yet. "
Timely snapshot/reality check. $.07 says "Exchange 14" will be based on SQL Server [2009?...].