Agree with almost everything mentioned... though in a tough economy and with a glut of courses I have no idea how most courses would be more inclined to herd people along, tell groups to skip a hole, etc. However, in a big enough metro area notorious for slow golf, I could see one course or another gaining a loyal following by being utterly ruthless about 4 hour weekend rounds. (Sad that a 4-hour public round should be a niche market, but there you go.)
Plus there's of course the 7-minute tee times and all the other things typically mentioned. (Bill Yates, if you are out there, do you have info on how much the avg design can add to the time - as opposed to tee time spacing, etc?)
But let me mention another idea... one that may have been mentioned before but I don't recall seeing here. Shivas may have touched on it before in some of his posts.
What about the possibility that some guys are *not* interested in a quicker round? (I say guys because most of the women I know are fast - if not very fast - golfers.) In other words, if guys get a hall pass, they can't play golf for 3.5 hours and then stay and drink beer with the gang for 2 hours afterwards, but they -can- play golf for 5.5 hours (and drink beer all the while). The idea being that "I'll come home as soon as we finish the round."
Say that Category A is what's typically referred to as avid golfers. Or call them true golfers, if you think the "avid" category is slightly different. These are people who play golf in order to play golf. That's different from those who play golf to get out of the house and maybe have a couple beers - Category B.
People from Category A are probably
1. more likely to know about ready play, etc.
2. more likely to join a club (and play more rounds), and
3. not motivated to extend a round beyond its intrinsic time
(which varies accdg to the person and course layout, but we can agree it is somewhere south of 4 hours)
For those solely in Category B, playing golf may be secondary. It's about Happy Gilmore impersonations, flirting with the cart girl, and not doing yard work. So why would they be in a hurry to finish? Category A says a round should never take longer than it should; Category B says it should never finish sooner than it has to. And it just takes one group to muck up the schedule.
Approaches to speeding up play assume that everyone on the course wants a faster round, and that's tough enough to achieve. But what if that assumption is wrong? What of some golfers don't care about faster rounds, and a few actually like the idea of an extra hour on the course?