I went to blockbuster to rent a 1 night DVD & a playstation 3 (2 night) game. The woman asked me If I wanted to do the 3 for 2 Deal, I said why not and grabbed another 1 night rental. Though under the 3 for 2 deal you keep all 3 for a week! I paid with 2 tesco vouchers as well! My son was thrilled 2 nights of a game is never long enough for him.
It is advertised in store, but I presumed it was on weekly rentals only.
I'm presuming it's nation wide, don't know when it started or when it will finish Sorry!