I've had this happen a couple of times when I've played with friends who are decked out with MF, and I have zero. I've heard that the percentages are averaged and distributed across everyone, but this doesn't seem to be a the case. On several occasions, my friends have been looted many more rares and blues than I have. Now, I understand that in general, this could just be how the cards are dealt regardless of MF. But it's happened with such frequency that I wonder if MF is actually shared or if that's a myth?
What it does, is add the total MF between the players and divides it by the number of players so if they are finding more than you, a lot of that could be to do with luck, that is the most important thing in finding good items in this game :P