I appreciate HHonors Representative starting this official thread. Made the link to register much easier to find (I think I must have accidentally deleted the email sent to me).

I registered a couple of days ago and was lamenting the fact that I had a couple of stays that occurred after the beginning of the promational period, but I wasn't able to register prior to the stays (was out of the country without Internet access). Fortunately, the points for one of my stays hadn't posted yet and I registered about twelve hours before the points posted -- the double points promotion was included in the posted points. Didn't think it would work since I didn't register before the stay began. Lucky for me, since I registered before the points posted, the promotion was still applied for that stay. Yay for me!