The only thing I really disliked about the flight out was that a flight attendant stood about halfway back and directed people to fill in the front seats before she'd allow passengers in the back of the plane. I wondered what was up with that...
When that happens there is usually some sort of weight issue. Planes are not stable for takeoff if there is too much weight in the tail of the plane relative to the nose. I was once on a half-empty United 737 leaving Denver; we were on the runway when the FA's came around and insisted that several large gentlemen who were stretched out in empty rows in the back move up front.
We voted for the current system. I like to sit in the last row & everybody else in the country seems to want to fight for the front row. It's usually pretty peaceful in the back on SW unless the flight is full. The tradeoff is that you will be the last one off the plane. Oh well.