Rules question - Ball tee'd up by someone else

Ok, I am happy with the rules situation, but how about another take on bladeplayers question.

If you were in the fairway playing your shot, and the person behind played from the tee and their drive rolled up 40 yards behind you, would you be bothered?

Does it make a difference that my ball rolled up just short of the green, even though it was the same distance away? Does the boundry of the green change peoples perception as to the acceptability of my shot?

Also what margin of safe distance should you leave, if 40 yards is not enough?