Friday Sept 5 according to an article in our local paper. I will try and dig it out of the trash and post the article here later tonight when I get a chance.
edit:
Was unable to find the article in question…but I found something better
The pricing seems to have affected the Arcade version:
http://www.ebgames.com/browse/search.aspx?N=0&Ntk=TitleKeyword&Ntx=mode+matchallpartial&Ntt=Xbox%20360%20Arcade
And the Elite Version:
http://www.ebgames.com/browse/search.aspx?N=0&Ntk=TitleKeyword&Ntx=mode+matchallpartial&Ntt=Microsoft%20Xbox%20360%20Elite