I always try to carry my bag with me.. generally two smaller bags that meet size requirements. I do this because I'm tired of having handles and wheels broken off (It was happening about one out of three times). A year or so ago I had one bag- well within the requirements- and the FA grabbed it from me as I boarded, because "the plane is full." I objected that my medications were in that bag. "Then you'll have to standby for another flight," she replied. I gave up the bad... and did not see it again for three days. So although I try to avoid carrying a lot on, I have a great deal of understanding for the reasons people do so on US carriers.