Can't vote right now, still weighing the pro and cons.
I'd jump on a GTX 280 any day at $449, I can say that though. A single GPU powerhouse that assures me 100% GPU utilization, which in itself is a value add. It would work for my requirements for a year, and if GT200b proves to be a near reality, it would likely be a $50 step-up option at most. EVGA/E-tailors need to bite the bullet and make the $449 price adjustment however. Gigabyte is already $449.
The 4870 X2 has advantages as well, as it appears to offer best in class performance. I like having the best available, and that also means having what's in demand. The main reason, I like knowing I can ebay it and have a strong buyer market when the time comes.
Clearly though, the GTX 280 has fewer cons than the X2. This is a battle of the psche, needs vs. wants. Gotta run... need to bang my head into the wall a few times..