OK, what do you get for signing up for a larger monthly fee on GoBank? The signup page lets you pick your amount from $0 to $9 with no indication a higher amount gets you anything more.
It doesn't, at least not directly. But if I thought GoBank was substantially better than all its competitors (I don't, at least not at the moment), I might be inclined to throw a few bucks their way in support. The idea is for it to be a way to motivate the developers to make a better product -- I'm sure the majority of people using it are paying $0.