I any large enough group, there is always someone scaming to eat free. Either that or they can't remember how many drinks they had. In big groups I've been in, we always come up short -- the tip is the first thing to go.
What I hate is when I have a credit card and everyone else has cash, and want to geive me monely to put it on my card. I usually discover that I have paid for a 10 dollar cup of coffee. Needless to say, I don't use a card with a group any more.