"Depends on the stores" is the single most important bit of information in this thread.
I was amazed to hear that Vision's BB had PVD's of hannibal, family man, shrek, unbreakable, and mummy returns for around $9. They range for between $12.99 to $14.99 at my BB.
Then again Bygdaddy tells us that Unbreakable and Castaway were $16.99 at his BB.
My personal guess is that Vision's is going to a company-owned store, and Bygdaddy is getting the well-known (around here, anyway) "Blockbuster Franchise Shaft".
The franchise stores are privately owned and are under no obligation to honor ANY BB "corporate" promotions. And they can't wait to tell you that. They set their own PVD prices and are usually a complete waste of time. I have a franchise BB five minutes from my house, but I do business with a company store about 30 minutes away.
The good news is (at least for me) that the store I deal with always puts the most liberal possible interpretation on any promo. When they have $2.00 off PVT "videos", they also honor it for PVDs. The franchises always say, "This is a DVD, not a video. No discount."
For this particular sale, they're doing Buy 2 Get 1 Free on ALL DVD's, new, used, mix-and-match, whatever. I have bought at least 25 titles since this started. And like Steelwells said, buying them in threes at the same price point maximizes your savings. This is a really incredible sale, I haven't gotten DVD bargains like this since Half.com had the $7.99 Netflix discs, and I only snagged two of those.