I don't know if this is still being updated, but I just picked up promo Thalia's Lancers at Wal-Mart. The second card behind it was backwards, such that the back of the cards were touching each other. Also, the other one I saw had a blue pack as opposed to the red (Born of the Gods), which makes me think Return to Ravnica.
The last 3 mailings I have are April 2010, October 2009, and July 2009 (I saved the paper that came with the cards).
I believe they say there's a general time frame when they are sent, but they start counting your points like a month early prior to sending. For instance, my last one (April 2010, which was sent in March) had enough for 5 but they started counting the points up in Feb. so I only got 3 =/
Edit: I forgot to ask, has the 2010 Holiday Promo been release? I remember looking for pics of promos and I came across one that had cost that included Black Mana, but I don't remember if it was current for this year or a past year promo.