FUD Zilla claims AMD's first Fusion processors will use a multi-chip module (MCM) instead of integration into the processor's die. The first truly integrated GPU/CPU chips aren't expected until the second generation Fusion processors arrive.
The second generation fusion might actually be totally integrated chip and this will eventually happen. Just remember the time when a floating point unit was a separate chip and this is the direction you should be thinking for fusion like products.
First generation will have two separate dies on one chip while the second generation might result in a CPU getting a GPU on its die. The best way to think about this is that this multi core CPU will get one or more additional core that will only take care of graphic.
Two months ago FUD Zilla wrote Intel's Nehalem processors will also use a multi-chip module approach.