One of the advantages to the cheap ponchos from Wal-Mart, Target, etc., is that you can simply toss them when the rain stops. They're less than $1 each.
It's much better than trying to fold up a bulky, drippy poncho after a storm and then having to carry it around with you. A few folks have said they didn't like the "thinness" of the disposable ponchos; they compared them to Saran Wrap. However, we prefer that to having to lug a wet Mickey poncho around for the remainder of the day. And at less than $1 each, you can bring several for each person.
An extra advantage is that they will actually fit into an average-sized fanny pack; in fact, I usually have two in mine, along with the other daily necessities.