I have been singled out at least 3 times by AA and AS for my rolly bag being "too fat" even though the expansion wasn't even opened in it. So, I have to take stuff out of my bag into my purse. I then see someone juggling 3 carryons (rolly, laptop bag, purse), food, coffee, etc. breeze past and use the overhead bin for all their crap.

I don't have a problem abiding by the rules, but gate agents do a pretty crappy job as a whole regulating carry on luggage (and boarding groups for that matter). That said, I see most people put the smaller bag under their seat. I only see a few idiots put coats up in the bin and those are usually squished around as more people board. In a karma sort of fashion...

/end rant