I must agree with Juno, I am currently just finished Undergraduate study and about to start a PhD in October. I am not the sharpest tool in the box and really bad at exams. But I have a hell of a lot of ambition and drive to get where I want to go.

My Prof. at my current uni always said he found that the best PhD students were those with 2:2 or 2:1 degree classes. He himself got a 2:2 at an unprestigious uni, and now he is head of a school at a very prestigious uni and one of the world leaders in his choosen field. His reasoning for this is that PhDs you dont have to be overly clever, but must be willing to work hard and those people with firsts thought that they were too clever to go through the laborious task of completing a PhD. In contrast, those with lower degree classes feel like they have to work harder.

This is obviously a very generalised statment.