They have more non Bitcoin related transfers now though. They seem to be growing fast,
Dwolla's model makes sense. $0.25 for a $100 transfer is much less than the $3.20 that PayPal charges. I've already had it happen where someone I've sent money to previously has now asked for the payment to be sent with Dwolla instead (to minimize the transaction costs). Of course,Bitcoin was the only reason that person had already signed up with Dwolla but kudos to Dwolla for being in the right place at the right time.
One of the worries that I had was that if Bitcoin were to start to take market share from the payment networks, would they simply lower their fees to lessen the cost advantage that Bitcoin offers?
Then I realized that Dwolla can actually take away some of the profitable business away from Visa/MC. The remaining business for Visa/MC will be the more problematic, less profitable transactions (merchants with a higher rate of chargebacks, customers who are paying with credit because they don't have the cash and thus might default at higher rates, etc.)
So Dwolla succeeding fantastically at the expense of the legacy payment networks will actually be something to look foward to. Going from one payment method (payment card only) to two methods (payment card or Dwolla) is much harder than going from two methods to three (payment card or Dwolla or Bitcoin). Dwolla can do a little trail blazing for Bitcoin.