So back to my earlier question - is setting a queue size expensive in the python implementation? If there isn't a technical weakness there, then I'm all for a) warnings and a migration point sometime in the future - it wouldn't be very costly to mechanically search and destroy all rospy.Publisher instances in a ros workspace. 

I agree with Daniel. Changing the default will break existing code, but if the default is undesirable in a non-negligible amount of cases, then it should be changed.

I would be in favor for a warning in Indigo, and a change of behavior in J-turtle.