I'm curious to see if they start enforcing it. It seems that they never give anyone any grief about bag size. And this is something I love about CO. My typical travel bag is a backpack which probably doesn't fit in the sizer, but is still smaller than the rollers everyone brings on boards and fits very easily in the overhead (the narrow way, which takes very little space).

If they do start enforcing it, I've lost the thing I appreciate most about CO (I hate checking luggage, even for free).