They have implemented larger caches in some of their newer processors, much more than a comparably-priced Intel. The FX processors (AM3+) have gigantic caches and faster FSB speeds. I'm not much of a sucker for other extended capabilities like 3D now or other onboard graphics instruction sets, etc. Also, the die manufacturing process can have an affect on the overall performance. The instruction paths are optimized to perform operations with fewer clock cycles.
Most people seem to be leaning towards more cores and CPU clock speed as the main selling points. However, more cores means less cache per core. I think if you're a gamer, a quad core with a large cache is the way to go, as most games don't use more than two cores, but a quad core will leave a little room for future developments or processes like video conversion that can dynamically take advantage of the extra cores.
Check out the benchmarks across the internet. There are many newer quad cores that outperform the hexacores and actually cost less. I would actually prefer a dual core if its cache were considerably larger.