It's clear by now that Intel has beat AMD to an effective quad-core solution by a significant margin. Coming this January, Intel will launch the first in their series of quad core CPUs, with AMD's answer still in the dark to many. For those that think AMD is slipping, however, there's a really good look into the AMD 4x4 platform that is just around the corner. While relying on two dual-core CPUs, the 4x4 platform seems to be specifically geared towards high performance in “enthusiast” applications:

AMD officials also spoke to their effort with 4x4 as a platform "inspired by enthusiasts". Multiple 4x4 processor bundles will be brought to market and although not officially confirmed, we've since learned that speeds ranging from 2.6GHz to 3GHz will be brought to the table.
AMD's approach to multicore is also far different from Intel's, in which Intel is much more reliant on having a speedy bus that all cores must share, whereas AMD thinks they have an advantage with independent links:

While Kentsfield in all likelihood will scale nicely in mutli-threaded applications and under heavy multi-tasking scenarios, the chip still shares a single front side bus, which unlike AMD's dedicated HT links for each dual core CPU, is a shared-bus architecture and potentially not as efficient.
AMD has a few more tricks up their sleeve as an answer to Kentsfield. While they now own ATI, AMD is still planning to use the very popular nVidia chipsets, though the exact name of which hasn't been revealed. Touting support for up to four x16 PCI-Ex cards and a massive 12 SATA II interfaces on a single board, it's a lot of hardware packed into a small amount of space. A coup de grâce to Intel would be the cost of two CPUs for a 4x4 system being less than a single quad core, but official pricing on compatible CPUs from AMD hasn't been announced yet. Given the price of the higher end FX class CPUs, that will be one difficult for AMD to pull off.