I do remember a recent flight, but it might have been on DL, where my underseat computer bag didn't fit due to equipment installed under the seat. Other than that it has always fit, although I often select bulkhead seats on AA, knowing I will have to put the bag up top. Fortunately I just bought a slightly smaller laptop which will fit in a seat pocket, and I haven't had any issues with FA's allowing me to take it out before I stow my laptop bag up top and leaving it in the seat pocket during takeoff.