Thanks for the details. I gather this is how they prevent weird inventory problems with stores, in that any disk you get from a physical store has to go back to that store.
Anyhow, it sounds like you're required to make at least 2 trips to the store then? One to make the initial exchange, and then the movie you get from the store has to be returned back to that store? Do you have the option of repeating this process, i.e. exchanging the "received from store" movie for another movie from the store instead of having the return trigger the next movie mailing? Or is it limited to 1 in-store exchange per pending mail return?
In either case, this isn't quite as nice as I was originally speculating. After watching a by-mail movie, it can be dropped in the mail anywhere (even in the outgoing mail at work), whereas the local Blockbuster isn't necessarily on one's way to work. Yet, you're required to revisit it to resume your normal mail movie processing, since that movie must go back to that store. I suppose that's the price one pays for being able to get a new movie outside of the normal sequence, so it's certainly better than nothing.