From Catholic World News:
Vatican, Jul. 6, 2007 (CWNews.com) - The Vatican press office has confirmed that Summorum Pontificum, the motu proprio regarding the broader use of the 1962 Roman Missal, will be released on Saturday, July 7.
Although some copies of the document-- which was sent to the world's bishops in advance-- are already in circulation, the contexts are under embargo until noon (Rome time) on July 7. CWN will respect that embargo.