AMD has been trailing Intel in the x86 performance space for years now. Ever since the introduction of the first Core 2 processors in 2006, AMD hasn't been able to recover and return to the heyday of the Athlon 64 and Athlon 64 X2. Instead the company has remained relevant by driving costs down and competing largely in the sub-$200 microprocessor space. AMD's ability to hold on was largely due to its more-cores-for-less strategy. Thanks to aggressive pricing on its triple and hexa-core parts, for users who needed tons of cores, AMD has been delivering a lot of value over the past couple of years.
Recently however Intel has been able to drive its per-core performance up with Sandy Bridge, where it's becoming increasingly difficult to recommend AMD alternatives with higher core counts. The heavily threaded desktop niche is tough to sell to, particularly when you force users to take a significant hit on single threaded performance in order to achieve value there. For a while now AMD has needed a brand new architecture, something that could lead to dominance in heavily threaded workloads while addressing its deficiencies in lightly threaded consumer workloads. After much waiting, we get that new architecture today. Bulldozer is here.