Blizzard is more famouse for excellence of execution than for revolutionary innovation. So sometimes we forget that World of Warcraft did in fact contain a couple of features that were revolutionary and new, and which caused quite some controversy when they were first reported on. Meanwhile we got so used to them that we don't even remember that these features haven't been around since the time of Everquest. One of these forgotten controversies is World of Warcraft's day/night cycle, which is based on a 24-hour real time clock, and not accelerated like nearly every other game.
When I first saw the 24-hour day/night cycle of World of Warcraft in beta in 2004, I didn't like it at all. But at that time the night was still a good bit darker than it is now, and I had to play with the gamma settings to see reasonably well at night. I don't know when exactly they changed that, must have been before release, but nowadays the night in WoW isn't really very dark. It is more a question of colors, the night being more blueish.
The main disadvantage of having a 24-hour day/night cycle is that it introduces real world time constraints into the virtual world. For example during the week I can only play from 6 pm to 10 pm, so all week long for me in World of Warcraft it is evening. There are few things in WoW that depend on the local time, but it isn't totally without effect. For example your chances of catching certain fish decrease or increase with time of day.
So while there are disadvantages of a 24-hour clock, Blizzard wisely chose to make the time of virtual day of very little importance, thus many people don't even notice the day/night cycle. Which in itself is a minor disadvantage, LotRO's Middle Earth world somehow seems more real by having a visible day/night cycle with much darker nights and monsters that only appear during certain times of day. But for such a day/night cycle to work, it has to be shorter than 24 hours, because you want people who only play a few hours still to experience it.
Do you think World of Warcraft would be better off with a lets say 4-hour day/night cycle, darker nights, and events and mob appearences related to the time of virtual day? Or do you prefer the way where server time is local time, and you can tell your real time by hovering your mouse over the little sun icon next to your mini map?