I am skeptical that anything big will happen tomorrow, for no other reason that it seems nothing happens when we are expecting it to (whether it's July 4th, the anniversary of Sept. 11th, etc.). What was most remarkable about 9/11 was that it happened on a completely normal day– a sunny Tuesday in New York and DC.

Here is Middle East scholar Bernard Lewis writing in the WSJ a few weeks ago on the significance of 8/22:

This year, Aug. 22 corresponds, in the Islamic calendar, to the 27th day of the month of Rajab of the year 1427. This, by tradition, is the night when many Muslims commemorate the night flight of the prophet Muhammad on the winged horse Buraq, first to "the farthest mosque," usually identified with Jerusalem, and then to heaven and back (c.f., Koran XVII.1). This might well be deemed an appropriate date for the apocalyptic ending of Israel and if necessary of the world. It is far from certain that Mr. Ahmadinejad plans any such cataclysmic events precisely for Aug. 22. But it would be wise to bear the possibility in mind.