From dulfy http://dulfy.net/2013/02/26/gw2-guild-missions-guide/
Guild Commendations are earned by participating in Guild Missions. You only earn them if you complete guild missions started by the guild you are currently representing.Currently it is speculated that you earn 2 Guild Commendations per Guild Mission but it is currently unknown what restrictions are in place (i.e. if there is a weekly cap etc).
My question is: Did anyone find out what are these restrictions? My guild did today 2 guild missions in different tier and we only got 1 chest…