FCFS in the back sucks. Pilots and Flight Attendants are at a huge disadvantage under this system because often times we are flying 24 hours prior and can not check in. I'm surprised I haven't seen people pointing this out to Doug and friends on the "crew news." The people actually moving the passengers from point A to point B are at a serious disadvantage.
I've also noticed on my 2 leg commute, if I have to take the jumpseat on the first leg, I lose my non-rev reservation in the back on the second leg. Seniority in the back was a much better system. The best open seats in back should go to those with the most service to the company, not those who have a faster internet connection 24 hours prior.