Even though much of the world's desktop software (particularly in Windows) isn't yet able to take full advantage of multi-core systems, the availability and cost of dual core processors have allowed them to be very quickly adopted. According to Intel, in 4Q 2006, more than half of processor shipments for were dual or quad core CPUs, for the first time ever surpassing their single core cousins. While they don't give specific model breakdowns, such as whether or not a higher percentage of desktop multicores are shipping versus server multicores, it's a very interesting piece of information.
Considering that now dual-core processors can be acquired for as little as $100, adoption will only increase.