What's the ideal MMO raid length?

I thought it was interesting earlier this month when Bungie explained Destiny's raids: They're smaller than what MMO players would expect from a raid (six players), but they come with some rather old-school MMO lengths, lockouts, and death penalties. One test group, the devs said, took 45 minutes just to get to the front door!

Bungie doesn't expect MMO-savvy players to take nearly that long once they've soaked up some internet guides, of course, but the article did make me wonder what gamers are willing to tolerate raid-length-wise nowadays. I remember giant raids that went on for days in EverQuest all the way up to quickie group-finder raids in World of Warcraft. Making them shorter (and cutting out the trash) didn't really make them easier or less fun, but it sure did enable more people to play them, which seems like a better way to justify the dev time spent on them. What do you think: What's the ideal MMO raid length?

TH