There has been some discussion recently on the FSDeveloper forum about creating a place to discuss X-Plane related topics as well. We have now created a poll to see how much interest there is to discuss addon creation for different simulators. Let us know what you think.
It is a long time ago that I looked at X-Plane myself, but I have been able to compare MSFS development with creating scenery for professional flight simulators (those that airliners use for their training). There are more similarities than you might expect at first. So I am sure that between FSX, X-Plane, FlightGear or whatever simulator platform there are also more similarities and opportunities to share knowledge then we might think at first.