What Can We Know About Judgment Day? (Galway, Ireland)

In the wake of Harold Camping and Family Radio's recent failed predictions, we got to thinking about what we can know about the end of the world and the great day of judgment.  Mr. Camping's prediction is just the latest in what is a long line of such hypotheses that have been submitted throughout the centuries. 

Among the many problems with such predictions is the over-stepping into areas in which the Bible does not speak -- a classic example of what God's word means by the following statement: "The secret things belong to the Lord our God, but the things that are revealed belong to us and to our children forever, that we may do all the words of this law" (Deuteronomy 29:29).  Mr. Camping and others purport to know things from the Bible, and yet a search of the Scriptures turn up no such information.

So, what does the Bible tell us we can know about judgment day?