In the past I've used ten questions to help people think about their branding, which you can see here. I've modified them quite a bit, and as a partnership we tend to use much more targeted questions. The reason I mention them is because one of them always generated a lot more information than the rest:
Do you have any competitors? Who are they? How are you different?
I've been constantly surprised by how some people could go into minute detail abbout a variety of competitors, yet give vague, bland answers to question like What exactly are your products and/or services? What qualities do they have? or What is your speciality?
I think people have got it arse about face, but perhaps it's no surprise why.