Zen and the Art of Ruby Programming:

DB2 Express-C for Mac OS X Leopard will finally be shipping out (before Christmas), in all likelihood it could be as soon as early next week.

Smart move – I don't expect anyone will actually run DB2 on a Mac for production, but it's obvious that the chance of developers using it increases significantly. I don't have any numbers, but I would assume that most Mac developers run their production systems on some flavor of Linux.