Related to this question, and applying both ways - finding a person is one thing, but for a technical founder trying to assess a non-technical founder and vice versa to see if they're a good fit is easier than knowing if they've got the chops.
My biggest weakness has always been giving people in non-technical specialties the benefit of the doubt. With technical staff, I've had a pretty good track record, and I've had the pleasure to work with great specialists who I can trust to give me feedback when I'm not as strong in a much further removed technical area.
Not so much with lawyers and graphic designers, to give an example. Let's not even start on sales and marketing ;-) (if they hoodwink me, I'm sure they'll do great with the customers!)
How do you assess talent in a field where you are not experienced?