Don't see many of them... the ones that get my goat are those that are sitting at the rear of the plane but put their carryon in the very first bin they get to in which it'll fit. This then creates the need to put the bags in bins behind your seat and thus the upstream swim issue.
The other day when I boarded our row, the one before and after on both sides were totally empty of people and yet our bin was overflowing with bags. On this occasion I only had a laptop bag so could stick it under the seat but I've more than once been tempted to remove other's luggage when its clearly not for those sitting near us and put ours in.