good post Mike, but: "DJ sets used to go for 2 or 3 hours on average and used to take you on a journey."
Let's say it used to go from 6 till 10h on average before the millenium ;-) It's a pitty those days are over at most venue's. Luckely in the underground scene there are a lot of exceptions and dj's get the chance to play all night long sets again...