One thing airlines should pay closer attention to is amount/size of carry-on luggage to better match overhead bins capacities. I've seen people bringing clearly oversized roller bag, AND big laptop bag, AND big purse, and then spending a lot of time trying to place all of that in bins, or under preceeding seat, blocking the aisle while doing so.

That's also the main reason why I try to board as fast as possible - to ensure that there's still space for my luggage.