Here comes the binary package for FlightGear/CVS as of 2009-05-19. The main features in this release are:

• Model View
  • enables you to see other aircraft models on Multi Player servers.
• Wildfire integration (see Environment >> Wildfire settings from the menu)
• JSBSim update as of 2009-05-10
[...]

I've released the GUI launcher updater for 1.9.1, which is available from here.

The updater fixes the following issues:

1. FlightGear might not be invoked due to misconfiguration of FG_ROOT (data directory)
2. Some options like aircraft and airport are not properly parsed, and c172p and KSFO are used even though you specified other aircraft or airport.

Please install it from Advanced Features >> Others >> Install Add-ons from the GUI Launcher. And then restart FlightGear.app.