Honestly, I don't get the whining about this. United agents and FAs are particularly anal about carry-on limits. I've seen FAs try and tell people they are exceeding their limit by having bags with food from the terminal in them (they aren't. That is specifically excluded). Camera bags are similarly excluded, yet I see people prodded about that as well. Also, because of the TSA madness, people are often unbundled when boarding (that happens to me from time to time).
Really, number of bags has never been the problem. The problem is size. FAR too many people, including rather frequent flyers, carry on bags that don't fit properly in overhead bins. If everyone had bags that fit wheels/handles first, gate checks would be significantly reduced. Similarly, unless you are in a bulkhead, you don't put the briefcase/laptop in the overhead. You put it under your seat until you know there is room up above. That would help things as well.
I had a roller that didn't fit well on the Airbus wheels/handle first, so I replaced it. Then I got rid of the wheels altogether. I carry as much or more in my bag and have a smaller footprint. Its really about courtesy, not enforcement. And what they do enforce is not the real issue, because the vast, vast majority of people don't exceed the carry-on limits when it comes to actual number. I do, however, see someone dragging a 24" roller or an overstuffed 22" expandable on every flight.