Hi Stealth,
You certainly hit on a weak spot in JW teaching. The 607 date and everything built on it is simply fluff.
If you want the full story on why the Society is wrong on this issue, get hold of the book The Gentile Times Reconsidered by Carl Olof Jonsson. The Society has never refuted Jonsson's arguments. You can order the book from Commentary Press at: http://www.commentarypress.com/booklist-eng.html
While you're at it, I highly recommend purchasing the following books (you can look up descriptions on the appropriate websites):
The Sign of the Last Days: When? by Carl Jonsson
Crisis of Conscience by Raymond Franz
In Search of Christian Freedom by Raymond Franz
Apocalypse Delayed: The Story of Jehovah's Witnesses by M. James Penton
These books are absolute musts for anyone wanting to understand why so many Watchtower doctrines and policies are based on nothing more than the dreams and guesses of old men.
If you're interested in a detailed look at the date change from 606 to 607, look at the article "The Evolution of 606 to 607 B.C.E. in Watchtower Chronology" and several related articles here: http://www.geocities.com/osarsif/index2.htm
AlanF