It’s why Kyle Reese Came back from the future to stop. It’s what Sarah Connor Raised John Connor to fight… and now it’s almost here.

According to the lore set forward in both the Terminator movies and books, Skynet officially goes active at 20:11 on April 19, 2011.

The ensuing Judgment Day – or at least the changed date for it after Terminator 2 is April 21, 2011.

On an interesting side note. There are several sects of Christianity that believe the biblical Judgment Day will actually occur on May 11, 2011 and that the subsequent destruction of the world by fire shall occur on October 21st of this year.

Source: Terminator wiki