8 Cores in a MacPro

Intel has already planned to release before the end of the year a 4 Cores CPU based on current Xeon core architecture. In reality it "only" requires to put 2 DualCore chips together on the same die. Anandtech has been able to test such 4 cores CPU, aka Clovertown, and has installed them in a Mac Pro.
As shown above, both the Mac Pro and OSX are ready to support and work with such CPUs.
We will see more and more multi-core CPU in the future, but it does not mean that we can really benefit from such processing power. Indeed software will have to be written in a special way to get the most of those future massively parallel architecture.