The Rapture, in which all devout Evangelical Christians are supposed to be "seized" up into Heaven by Christ, was supposed to happen today at 6:00pm whatever time. Problem is, the Rapture has a long history of not happening, dating back to just after the Crucifixion, around 2,000 years ago. There's also the little thing Jesus said, in Matthew 13:32 and elsewhere, about even him not knowing when he's coming back because that's for only God to know. But don't tell those Evangelical pastors with their Bible maps, Bible codes, Pyramid inches, and convoluted numerologies like the one Harold Camping, Christian radio millionaire, used to precisely date the Rapture to today at 6pm whatever time. They know exactly when the world is scheduled to end, right down to the second. Even though only God's supposed to know such things.
The Rapture is not actually in the Bible itself. Rather, it's extrapolated from various scattered passages in the notes of Cyrus I. Scofield, whose Scofield Reference Bible is the bible of Dispensationalism, that school of Evangelical Christianity started by John Nelson Darby, founder of the Plymouth Brethren sect. It holds to the strictest historicism in all Christendom, particularly concerning the origin of the world (creationism is one of its core tenets) and the end times (eschatology). The "Bible map" phenomenon which became so familiar to me years ago when I watched Christian TV, in which the whole history of the world from the six-day Creation back in 4004 B.C. to the future Eschaton is precisely dated and placed on a timeline, is wholly Dispensationalist. Dispensationalism is not an orthodox Christian doctrine, but a strictly Evangelical one, and one not believed by all Evangelicals; non-Dispensationalists, including those Evangelical sects not influenced by the Brethren movement and which reject the Scofield Reference Bible, consider the doctrine heretical. But it's a major force in American Christianity, which is overwhelmingly Evangelical, particularly in the South and parts of the mountain West. As long as this is the case, you'll keep hearing about the Rapture a lot.
What we're witnessing here is yet another in the long series of Great Disappointments that plague the history of American Evangelicalism, the most famous of which is the Great Disappointment of 1844 which destroyed the Millerite movement but, amazingly enough, spawned a host of new sects from the Seventh-Day Adventists to the Jehovah's Witnesses. The next one is scheduled to hit the New Age movement, a religious group not normally susceptible to Evangelical manias, on December 21, 2012, according to the "Mayan calendar code" of José Argüelles, the guy behind the Harmonic Convergence of 1987. December 21, 2012 is when the Mayan calendar is supposed to end, you see, and the world with it. I'll post here about it the day after it doesn't happen.