I can answer that question, I just received a confirmation e-mail saying my app qualified for a free tablet YAY!! I wasn't at all confident my simple concept would be enough for them to consider it a full game, or worthy of a tablet, but they did so great!
But I didn't get the qualified e-mail until I placed my app on the store system, about 12 hours later I received the notification that I was entitled to a free tablet!
So the process as far as I can see it is.
1) app is approved
2) app is added to store by user
3) considered for free tablet
4) confirmed or rejected for free tablet offer and shipping information is requested.
In theory my shiny new playbook tablet should be shipped within 72 hours, I dare say they are using a super economical courier service for this so it might be a few weeks until it shows up. But when it does, I'll certainly post it's arrival on here!
* does the new tablet jigg *