At sculpt a random model, for example the cube subdivided 3 times, and sculpt with mouse button hold pressed moving around for 3-5 secs or more start use the 100% of CPU and other programs stop like music player, chrome audio...
*In the 2.70a release version x64 this only use the 15%-30% of cpu at max.
CPU: Intel i7-4770K @ 3.50GHZ
RAM: 16 GB
GPU: Nvidia Geforce 780 GTX
OS: Windows 7 Ultimate, 64-bit, service pack 1
Drivers: Nvidia 337.88
Blender: 2.71 Release x64