I registered for the 5000 pts for 2 stays - max of 25k points Megabonus. I had 3 stays post recently (check in 14th, checkout 15th, then 15th to 16th, and 16th to 17th).

5000 points posted with "2009 MEGABONUS PROMO - VISA" in the description column. Also, my promo progress tracker shows 2 stays and 20% complete for the Megabonus.

So it appears that the stay where I checked in on the 14th and out on the 15th does not count. I guess this makes sense since the promo starts the night of the 15th.