I recently had a technical interview where I stumbled the whole way through, but I kept my attitude lighthearted, asked plenty of dumb questions, and am pretty sure I even said "Oh, geez, I'm an idiot" at one point. They acknowledged that I was a weak candidate, but they liked me enough to extend an offer amounting to a 33% salary increase over my current job--and with an additional 33% bump after 6 months if I can prove that I am actually not so much of an idiot. :)
Humility and earnestness can go a long way. A big ego never helps.