As RJR said, you can overclock the multipliers on the K series chips for Sandy Bridge coming in DEC/JAN
Clock rates are determined by a crystal which sets a frequency, a series of logic chips can multiply and change that frequency output. Currently, there are several crystals and even more logic in chips in order to accomplish the various frequencies needed. Intel is trying to only have one base crystal and a variety of multipliers to get the buss speeds for the CPU, RAM, PCIE BUS, SATA BUS, etc. As more and more of the "chipset" moves on the the CPU, this simplifies their design.
You will still be able to adjust the multipliers for Memory, and (for a K series chip) CPU.
The problem is that your HDD will go haywire when you overclock it (since everything will be connected, when you OC your CPU via the base frequiency, your USB, HDD, etc will also overclock). It's possible motherboard makers will find some workaround, and it's possible that the Socket 2011 Chips won't have this limitation. We'll all find out all the details over the next month or so.