Arwinphoto, I'd buy the 5D MK II now. At $2,000 its not going to decrease in value for a long time, used ones go for that price. I have the 5D MK II, a 7D, and just sold my 1D MK III. All are great cameras, but the 5D is the one I grab for general use, and the 7D I have for tethered product photography use in my studio, as a backup body, and for birding or sports.
I'm toying with the idea of pre ordering a 1D X, but haven't decided. I'll probably wait to see what else comes along.
The cost of developing a new FF sensor is said to run a billion Yen, so Canon may be using the sensor in other products as well, rather than develop and support two FF sensors. Supporting a separate FF sensor is pricey, separate software, hardawre spares, and a whole host of extra expense, so 5D MK III might just have the 18mp sensor as well, and the autofocus is fine for my use.