By all accounts, Harriet Miers' intelligence is not at issue, but her judgment is.
There are many people whose intelligence is non pareil, Helen Calidicott and Barbara Ehrenreich are just two names that spring immediately to mind, but who I would never even think of entrusting with my future, or the future of other Americans.
Only by reasonable people. The truth is that John Podhoretz is literally questioning her intelligence (more than questioning, if you ask me) and JCEccles stated "she's an intellectual lightweight".
But, being a mathematician is more important than being an engineer (pretty hard) or chemist (sorta hard) or physicist (pretty hard) is the ability to engage in abstract thinking. Stephen Breyer told us that he is incapable of engaging in enough abstract thinking to understand that the Constitution might be a little applicable to modern life. To the mathematician, all of the other sciences look exactly the same, just different names for the same stuff.