I don't live in the States and so I am not intimately familiar with how Dwolla works, so what makes them special? How are they different from other payment systems like Paypal? Why can't a Bitcoin company replicate their success?
My understanding is that they operate outside of the traditional banking system they're essentially in the process of setting up their very own financial payments network. Not sure of the actual nuts and bolts, but part of their mission is to provide super-cheap transactions, because in their most basic form, financial transactions are simply exchanges of data. Anything under $10 is free, and anything over even millions is only $.25.
This is really a bummer for those of us in the States. Dwolla rocks.