I usually book at 11 months out because at least one, if not all, of my tickets have been award tickets. For my trip this past July, I had enough miles for 3 of 4 award tickets. In order to guarantee that we could all sit together on the same itinerary, I went ahead and booked that fourth ticket at 11 months out as well and paid the exorbitant price of $1100 RT for coach/$1800 RT for coach/FC combination. However, I checked often and the price of those tickets NEVER went down. (Learning: Airfares, rental car rates, etc. peak in July. Avoid that month if you can.)
The AMEX 2-for-1 flights do, indeed, earn FF miles, but you cannot pick the airline nor can you dictate your itinerary (though some have reported that the agent worked with them to do so). AA seems to be the carrier of choice lately. And they only fly from mainland to HNL, so if you're headed to Maui, you have to add in the RT cost of that as well.
All things considered, I didn't find the Plat AMEX to be that great of a deal for me. However, with airfares now double what they used to be, and the cost of award tickets increasing, I may have to keep the AMEX option open when I go to book my 2010 trip to Maui.