It seems the promotion for the free weekend of play in Steelport has been a little premature as there's little official information but 'Sep 2012 (Complimentary)' receipts are showing up.
These can be found in the purchase history. More information is available via the official Saints Row: The Third. Volition is busy developing Saints Row 4.
Saints Row: The Third in "free weekend" promotion on Steam
19 September 2012 | By Simon Priest