I really liked the way Klaus termed it: a campaign setting should remain a snapshot. As such, I voted no on the metaplot.
So long as there are new places to detail, people to describe and organizations to flesh out, metaplot is a bad thing. I want a campaign setting to give me story seeds and plot hooks, but I don't want it to resolve a single one. I want adventures detailing these plot hooks, but I don't want the adventure to be canon. If the campaign setting says it's day one of year 1000, I want all the accessories and supplements to assume it's still day one of year 1000 (except for in the adventures, mind you, which aren't assumed to have happened yet, anyway).
So we get a look at the world that day. We see that, say, the Demon Lord Flub has been imprisoned for the past century in a statue within the holiest city in the world.
Then we detail the city that day. We find that he has cultists working to free him who have infiltrated the church hierarchy.
Then we get a look at the church. We discover they were formed 1000 years ago and there's a prophecy that one of their own will eventually herald the Age of Flub or some such.
At no point, though, does the timeline advance. Flub remains imprisoned. The cultists aren't routed out. The Age of Flub doesn't come to pass.
The setting gets detailed, but none of the plot hooks get invalidated. If you want to run a game around the release of the demon Flub, you won't find that, in the city book describing him, he's been released due to book X. When you read the book of cults, or whatever, that cult is still there, still doing its business.
I want a campaign setting to give me ideas. To get the ball rolling, then letting me take it the rest of the way.
Sure, I don't have to use metaplot elements. But the more metaplot there is, the harder it is to ignore. And that's when I stop buying books.
So long as there's more setting to detail, metaplot doesn't even serve the purpose of making new books. Once a setting has been described in full...which is effectively never...then start with the changes. Otherwise, leave them the heck out.