I am also of the carry-it-on breed, usually with two bags (rollaboard and computer bag, both heavy). Sometimes because I don't have the time to spare, and other times because I do not trust either the airlines to deliver the bags on time, or the honesty of the luggage handlers (personal experience).

I have had occasional problems with UA during my rare domestic flights about 3 vs 2 bags, but usually I win. In my early days with TG, I would sometimes have problems if I were flying econ on a short flight where they would allow me only one bag. Once, I was flying back to Bangkok on TG (from where I forget... probably some SE Asian country) and was intercepted on the stairs as I was getting ready to board the plane. The TG ground crew (most probably contract workers) said I could only take one bag. We got into a protracted discussion. I was not in the best of moods at the time, and told the guy I would call TG management in BKK. He said go ahead, and checked my bag on the tarmac as I was calling. Well, I did make a bit of a stink with TG HQ, and they actually called ops at the airport. A carnationed TG rep drove out to the airplane, boarded, and tracked me down, and apologized and said that they would gladly hold the flight while they got my bag out of the hold and brought it to me in the cabin. (I am amazed that I can remember all this, yet forget which airport it was.) You can all imagine that I was a bit embarrassed, told him it was OK, and that I simply expected to see my bag back in BKK in a timely fashion with contents present and accounted for. No problem... bag arrived, nothing stolen, and from then on my TG record bore notations about me and my bags