I am new here. I have read this thread with a lot of interest as slow play is definitely a pet peeve of mine, particularly when it's caused by players who are clueless (and not deliberately trying to be slow... or important!), for which the remedy is simply education. It galls me even more when neither the course nor the leadership of a group (e.g. in multiple groups play such as tournaments) does anything to enforce guidelines/rules or educate.
I walk about 80% of my rounds on week days and have played anywhere from 2:30 to 5:30 on those days, and I can definitely say I am not the reason for this large of a difference. I have played as a single in 4:15 and played as part of a five-some in 3:45. You name it, I have seen it... all the way to 6:45 rounds (I wanted to go home so bad!)
I am also playing in an associate club (roaming club without real estate assigned) that organizes tournaments on the weekends, riding, thankfully! The format is stroke play and every hole needs to be putt out or you are DQ'd, which sometimes leads to scores of 12 or over per hole. This group routinely plays in over 5 hours. The previous leadership was trying its best to sensitize people to the issue and educate them on how to be better and it worked to some extent: recording the finishing times was an incentive as nobody wanted to be in a group finishing 20 minutes (or worse!) after the previous group. The new leadership won't do any of these things and in fact the president himself admits that he is a bit deliberate (code word for slow!), yet routinely gets paired in the first or second group out and sets a bad example for everyone, and a bad pace for the rest of the tournament, not to say anything about the poor souls playing after us. The excuse is usually, we are not as good as you, and yes there are some really high handicappers (we range from about 5 to 36.4) in there, but I don't buy this as being the primary reason why. Yes, it is a factor, but poor cart management is the biggest culprit in my view.
Anyway, in 2014, I played about 120 rounds overall, with 23 at or over 5 hours, most of those long ones playing with that crew (I think we had 15 tournament rounds that year). I have threatened to quit over this (and other shenanigans). I was indeed determined to do so, but haven't yet found a suitable replacement club in the area, so I have re-upped my dues for 2015 (I am getting a GHIN index through them). I'll bring it up again... and again, until they do something or ban me... but it can be stressful. I have learned to be more patient on the course (inside or outside this group) and I am pleased when a round finishes in 4 hours or under.
Sure, if I was in a cart as a single, I could zip around under 2 hours, but I am not trying to do that, at sunset or whatever... I don't mind people doing that, just don't expect to do it on crowded muni courses on a weekend, and certainly not behind one of our tournaments. I am sorry for the latter part, but there isn't much more I can do about it...