<<I probably wouldn't do it if I had to pay the full retail whack...But I don't :)>>
Nor do I,the price of the GTX280 fluctuated a lot since it was launched,I waited until the right moment and got them both from dabs.com at a price which I believed I'd saved around £300 if compared to the price they charged at launch.(The price went up again afterwrads)
And I believed I didn't pay very much more than what you'd paid for your twin 8800GTX year ago. :0)
"For a complete ATI CrossFireX™ system, additional ATI Radeon™ HD 3800 series graphics card(s), an ATI CrossFireX Ready motherboard and one ATI CrossFireX Bridge Interconnect cable per board (included) are required"