Chicago Mercantile Exchange Holdings Inc. (NYSE, Nasdaq: CME - News) announced today that it has established May 29, 2007, as the record date for the July 9, 2007, special meeting of shareholders to vote on its proposed merger with CBOT Holdings, Inc. (NYSE: BOT - News). Part of the deal is that they will buy back up to $3.5 billion of stock, or 12 percent of outstanding shares, for $560 per share -- What determines who will get the $560 per share. How does this actually work out ? Is anyone actually guarenteed to get the $560 like they are guarenteed to get to vote on July 9th....