The Neverending thread and the Two Truths and a Lie thread have been very popular, but are they worthy of consideration as The Greatest Thread of All Time? Methinks, not. They are fun, but lack the level of thought and creativity that have had to go into, oh, say, the Photoshop thread or the Haiku thread.
I propose that the great minds of Cyburbia collaborate to write the Great American (and non-American) novel. We will each take turns in writing the next sentence or two, thus producing, well, something.