Hey all, if you are interested, one of the FSX_Thunderbirds told me about this group doing multiplayer formation flying.
http://www.premaero.com/
It's a growing community of folks into this sort of craziness. (Because it's now past just silliness... )
Edit: Guys, I screwed this all up. Premaero is different from the Bluebirds. It's the Bluebirds that are boxed FSX only. Premaero is Steam and Teamspeak.