The real issue is that if a guy doesn't think a girl is attractive just because she's smart, then he's probably not all that smart himself, at least in the relationship world.
I would have to agree with the other answer.^ As a guy its a plus if anything. Intelligence often makes for good conversation. And also, if being smart is a turn-off for a guy, he's probably not someone you want to be with. The only way it would be bad is if that meant the girl looked kinda nerdy.