They're not a minus in and of themselves. But more than a few hiring managers will prefer someone who obviously worked hard and has a transcript that moves from a B/B+ average to A's the last several years than someone who has an A in every class they're ever taken. If you're not going into academia or research it's much less important that you be a genius and much more important that you're willing and able to put in work over months or years to achieve an objective.