UA seems to do a pretty good job at enforcing it. I noticed AS called certain preboards by name, in advance, but then just did the general preboard announcement and it was a free-for-all. They all better be in non-exit row windows so as not to impede an evacuation. If an anxious passenger needs preboarding, then please, a window seat near the back, because if (s)he's anxious then, what about in an evacuation. Bum knee? A row behind the anxious one. Unruly kids? For sure, way back.

Now, a week ago, I had a day trip where I had absolutely no carry-on, and I really didn't care when I got on the plane. But if I'm in rows 1 or 2 of a 734 or 73G, where the rollers don't fit in lengthwise, and I may have no underseat space, better believe I'm going to be onboard sooner rather than later.