SOME MORE BITS about AMD's CrossfireX architecture are leaking out, and it is about what you would expect. Up to four GPUs, mix and match to a degree, and one really bad part.
First the good stuff, starting with the most asked question, when. It is slated to come in the March driver drop, aka Catalyst 8.03, from what we are told earlier in the month. That lines up with CeBIT if you hadn't noticed.
On the more technical side, you can do 2/3/4 GPUs, and they do not have to be the same, although close is a good thing. The faster cards will more or less ramp down to the slower one but the memory speeds will not change. Memory disparity will cause the second card to wait every so often, so things are not running flat out all the time, but you should not notice any slowdown here. In any case, this is far from the end of the world.
What this means to you is you can put similar cards in the same box and get a speed gain. Similarly to Hybrid Crossfire, there becomes a point when the ramping down/waits will make the combo slower than the speedier card of the two alone, but as is the sign of any good architecture, it should work. You can off-road with your Ferrari Enzo if you feel the need, but don't expect good results. Look for the envelope of compatibility to expand with each new Cat release as well.
The most asked question is R680/3870X2 related, basically can you mix and match with those parts? The short answer is yes; internally the X2 is seen as 2x 3870s with slightly odd clocks. With a 3870 and a 3870X2, you will get 3x the clock rate of a 3870 and a little less than 3x the memory bandwidth of the trio.
In general, AMD looks to have done a decent job with CrossfireX, but the down side is that to me, it is about as useless as knobby tires on the aforementioned Enzo.
This means that the CrossfireX architecture will have to be completely redone if they want an XP version, something they deemed not worth doing at this point, and I hate to say that I agree with the decision, but I do. That said, because of this, you are never going to see more than 2 GPUs working on XP making CrossfireX pointless to anyone not liking the tools that come with Vista. That would be me.
In the end, you have a mixed bag. Technically, the architecture is cool, they hit all the right features for the right reasons, and if it scales like they promise, it will be a very good thing. On a technical level that is good, but the baggage that comes with it, MeII, makes me wonder why anyone would bother.