I boarded behind a not in uniform military guy (saw the ID on the backpack) yesterday who had a full-sized garment bag (double fold) and a large backpack; he asked the FA if he could place the garment bag in the closet by the door (MD80) and was accommodated. Apparently, he made it with those bags all the way to the aircraft at that airport (RDU). The backpack might have fit under the seat but it appeared a lot thicker than 9".

I noted, on all flights in the last week I was on, that 'free' gate-check was announced by the GA's. I also did not note any rejected carry-ons, except one on a USX SkyWest CR9, where the bag wouldn't fit the OH. Overall, very smooth carryon handling and this on full flights on narrowbody AC (738/MD80).