Macgasm first noticed that Apple has begun offering free copies of Mac OS 10.6 ("Snow Leopard") to paid MobileMe subscribers. The free Snow Leopard offer was presumably initiated to encourage people to upgrade to iCloud before MobileMe is shut down on June 30th, 2012.
Neither my wife nor I -- both long time MobileMe/Mac.com subscribers -- received the invitation. But we've both already made the switch to iCloud, so my working theory is that only MobileMe laggards who haven't yet made the switch to iCloud are getting the invitations.
Regardless of being invited or not, any active MobileMe subscriber can still obtain the offer by going to www.me.com/snow-leopard. Curiously, Apple is fulfilling the offer on old-school boxed DVD media and not digitally via the Mac App Store.
The free cat offer expires on June 15th, 2012.