I was prepared to buy the GTX 260. With its specification I thought it would perform very well. However, there were rumors of a price drop because of the incredible performance from the 4870, and I waited. I am glad i did, the 4870 performs better than the 260. There are a few negatives though, the 4870 is much much hotter and consumes loads of electricity.
From my experience CFX has been greater than SLI, but it varys between person to person. I would have to say the 4870 is the card to buy.
When the new ATI cards were released it seemed pretty clear that they were the better values across the board at $200 and $300 respectively, but with the recent Nvidia price cut bringing the GTX260 down to $300, how does this affect your choice between the two?