But this is my biased opinion as a Bitcoin user (and former Dwolla user). Please go read about it yourself. Perhaps others will come to a different conclusion.
I run Bitfloor and was hit with similar fraud as Tradehill (on a much much smaller scale) and Dwolla was just as ignorant and dismissive of it. Fundamentally, they went into a business that they did not understand. I know this to be true because early on (even before any Tradehill incident) we emailed them to ask about ACH chargebacks and how they handle them. They claimed there were no chargebacks and this was everything I needed to know about their lack of understanding.
A while back I recapped what happend between myself and Dwolla and why they are not a useful service.