The Thanksgiving-Washington Myth

Perhaps myth is over-stating it, but you may have seen something floating around the Internet, perhaps emailed by a Christian friend, that reads as follows:


It is the duty of all nations to acknowledge the providence of Almighty God, to obey His will, to be grateful for His benefits, and humbly to implore His protection and favour...requefted me "to recommend to the people of the United States a DAY OF PUBLICK THANSGIVING and PRAYER, to be observed by acknowledging with grateful hearts the many...favors of Almighty God... -George Washington


If you Google this quotation, you will get many hits to Christian web sites, most of which are attempting to make an in-your-face-Secular-America! case that George Washington was overtly religious and on record as essentially ordering the United States to pray (presumably to a Christian god).  
There are several problems with this interpretation.  
First, Washington did not actually write these words.   Although he did sign a similarly-worded proclamation at the request of Congress, the historical background is more consistent with Washington's Deist impulses.  Washington generally eschewed and mistrusted overt expressions of religiosity, as did most of the founders, who were much closer historically to the religious wars and mass murders that convulsed Europe shortly before the founding of the United States.  All were steeped in the ideas of John Locke and Voltaire who railed against the dangers of religious excess, especially of a Christian variety.
Second, William Jackson, not George Washington, wrote this document (although George Washington signed it).   He wrote it not because it would have entered his head to do such a thing but because some members of Congress requested it (although others felt is was intrusion into a personal and religious affair, or mimicked the fake compulsory shows of thanksgiving demanded by European monarchs).  
Third, the actual statement he signed (see below) has been altered by religious apologists wanting to make Washington appear to be more religious than he actually was.  I have included the complete paragraph of the proclamation in question, highlighting in red the alterations made in the circulating Internet version:  

Whereas it is the duty of all Nations to acknowledge the providence of Almighty God, to obey his will, to be grateful for his benefits, and humbly to implore his protection and favor, and Whereas both Houses of Congress have by their joint Committee requested me 'to recommend to the People of the United States a day of public thanks-giving and prayer to be observed by acknowledging with grateful hearts the many signal favors of Almighty God, especially by affording them an opportunity peaceably to establish a form of government for their safety and happiness.

Washington did not capitalize pronouns referring to "Almighty God" as a Deist would not generally do (he did, however, capitalize Nations).   This insistence on avoiding overt religiosity among the founders was fairly consistent; the Declaration of Independence makes a vague reference to "Nature's God" and a "Creator" but does not capitalize any pronouns related to this creator either.  The Constitution does not mention God at all.  Washington is elsewhere on record as stating that the United States is "in no ways a Christian nation." 
A full text, showing Washington's actual spelling and capitalization is available at the Washington archives or the University of Virginia.