AMD has proven itself, successfully launching the Radeon HD 3870 X2 on schedule, and perhaps even more important than that, having actual products on retail shelves immediately.
The ATI Radeon HD 3870 X2 is essentially two Radeon HD 3870 GPUs stuck together on the same PCB. The GPUs use a PCI Express 1.1 bridge to communicate in much the same way Crossfire ATI cards would. However, because the X2 is meant to be a "transparent" single card solution, it doesn"t require a supporting motherboard, and in fact it opens the possibility for quad-Crossfire using two of these graphics cards.