Excess carry-ons are my major pet peeve when it comes to flying. I had four hours before my flight from Philadelphia about a week ago, and watched as pax maneuvered luggage on and off the planes. A couple of pax had so much they had to find a cart to transport it all.
I can't take credit for this next idea...I read it on CNN, I think...yet, it's one that might work. Allow checked bags to ride for free (up to a reasonable weight limit) and charge for carry-ons. That should clear up some overhead space!