http://www.rockpapershotgun.com/2011/06/09/arma-2-free-bohemias-opus-for-nowt/
It's not OA, but it's an incredibly bold idea!
Fantastic idea not bold becuase i think it will intise people to buy the full game
It might well encourage community members who don't currently play ArmA 2 to have a go, buy OA and then join us on the server. Good call.