Good news! FlightGear version 0.3.11-pre1 builds perfectly well on OS X (Tiger). The dependencies are plib and SimGear. You should install plib via macports (the 1.8.4 upstream tarball fails to build, CVS might fare better), then compile and install SImGear version 0.3.11-pre1, then compile and install FlightGear and grab the fgfs-base package and move it to /usr/local/share/FlightGear.

MacFlightGear works too, version 0.9.10. It will probably have an 0.9.11 release sometime not long after the release of 0.9.11 (if not sooner), because it would be hard to justify not releasing it when FlightGear builds out of the box. You might like the one-download no-build nifty-gui-launcher aspects of MacFlightGear. I don't because it messes with .fgfsrc and I like the consistency with Linux. But we never said I was sane.