Media event set for September 9, launch likely ~10 days later.
Apple Begins Preparing First Mac Pro Orders for December 30 Delivery
Although the majority of users' reported dates appears to be December 30, a small number of users are also reporting that their deliver dates are December 27. Both dates would squeeze the new Mac Pros into Apple's self-imposed December release date for the new professional desktop computer.
It appears that the first shipments of the Mac Pros are all stock configurations, as it has thus far been unclear if custom configurations have been shipping out to users. Since online ordering has been available, the shipping estimates have slipped into February 2014, with demand outstripping supply.