I would say 2-3hrs early. 2 hrs being the absolute min. I flew out of LAX in Mid-oct and missed my scheduled flight 'cause I only got there an 1.5hrs before the flight left. This was a flight from LA to Indiana, btw.
Lethal
EDIT: What takes so long is that everyone has to check in at the counter. No gate check in, and not curb side luggage check. 75% of yer time is spent waiting to get to the counter to check in.