What keeps me, the bitcoin trader, from being screwed by the transfer services and exchanges? Competition. Exchanges are competing to offer better methods of transferring USD. Competitors include cash, checks, money orders, ING Direct P2P, Popmoney, ACH and bank wires.
Yup, Dwolla used to be the method with the least friction. They introduced friction (probably were forced to by their new investors) and as a result, it took a mere matter of weeks for an explosion of alternate transfer methods to be implemented.
Mt. Gox used to be the exchange with the least friction for many. The Dwolla restrictions plus other service failures (whether they stem from cash management or policy changes, etc.) have cause Mt. Gox to no longer necessarily be the exchange with the least friction, so we are learning how to route around the damage.
And BitFloor is the most innovative and solving this friction problem. (Cash deposit at a bank, with no fees, with fast (same day) credit to my BitFloor account, ... I like very much!)