It's certainly an interesting idea, especially if it was combined with the new CrossfireX technology they've been talking about to let you use Crossfire between an ATI card and it's onboard graphics.
Imagine what gamers would do for a motherboard and chip combo that offered an approximate 20-30% boost in performance in most games, for around the same cost as a typical enthusiast board and dual core chip.
Sure, it'd be a bit of a cheap trick, but it might be another way for AMD to lever themselves into the mid level market.