The only thing I can find is this blog entry: http://www.dwolla.org/blog/dwollamarket-day-design-contest-extravaganza/
Where it states that only the winner of the contest gets a free t-shirt (with their design on it)
Pretty crappy contest if you ask me, hey do our graphics design for us and we'll give you your work back as a prize to help us promote our brand!
Makes me want to start a contest for the funniest ridiculing/making fun of dwolla t-shirt and the winner gets a tshirt as well as one for myself, lol
(I am not making that offer, I am just tempted to because of the idiocy of such a contest prize)