R680, or two RV670 on the same PCB, should come out in late January, while the real next generation high-end is scheduled for Q2 2008.
There aren't any delays, at least not that we know of, and this new chip is a big hope of ATI. The company has been trying to dethrone Nvidia for years and it hopes that R700 can be the next R300. This might happen, but Nvidia has managed to be one step ahead of ATI for years.
ATI managed to get back in the game in 2007, where it took back significant market share from Nvidia, mainly due to better prices, but it needs faster high-end products to compete against Nvidia even better.
Nvidia would be in real trouble if R700 managed to beat G100; but usually Nvidia knows what it's doing.