It makes it soft and silky, Wendy, and keeps it nice longer. It isn't that noticable at first when it is missing, but after a few days the stuff without cream of tartar starts to dry up and harden a bit, and leaves gunk on your hands. Not enough to make it less fun, though, so leave it out if you want to. I used to make a new batch for my Kindergarten class every week, and always left the cream of tartar out because I had to pay for all of my supplies and I wanted to throw away the dough frequently anyway to cut down on germs in the classroom.
