We just got back from a split stay at POR and Poly. The offer was in my room at the Poly when we checked in on 8/31. That seems to be the magic date when the offer started appearing. Not sure if it was in all rooms, or those with room only rates like us, but sounds like all rooms. It did have a code associated with it, and the CM checks your reservation in their system before giving you a quote. We were on the ME bus back to MCO and the CM was giving me a bit of a hassle about being post-checkout...
We booked a return to POR from 9-13/ 9-20. The CM wouldn't break out the room rate in the package, but did quote us the MYW ticket prices from the WDW website. If you take those full price tickets out of the total price and divide by the number of nights, we got a room rate of $174 at POR, including tax. Which sounds pretty close to $155/nt base rate...
I'm still hoping for a better room only discount at the Poly, and we'll just skip the modified Free Dining plan in 2008, but wanted to book POR just in case a better Poly offer doesn't come along!