I was perusing this thread, and I realized I may be able to answer two of the questions some of you have asked, so I created an account to do so.
I got an email from the customer service of the promotion stating the following:
"Your 3x5 should be in an envelope and everything, including the destination and return address should be handwritten."
So that means no postcards either, at least according to the individual who dealt with me. (They didn't accept my reasoning that having no envelopes to open will save them incredible amounts of time.) Presumably, some will respond with a YMMV or DROPR (DROER).