The Clarkdale CPU represents an evolutionary step in the CPU; this is a move to a combined CPU and GPU. It is something that NVIDIA and AMD both want to do as well. However, neither AMD nor NV can do anything about it right now. NV is locked by the lack of an x86 license and AMD is not in a position to make this move due to financial problems that have hindered R&D. This has allowed Intel to get off the opening shots in the CPU+GPU wars that are soon to follow.
Of course, there were things that had to be done before this was a possibility. The first was accomplished with Nehalem; the moving of the memory controller off of the Northbridge and into the CPU. The next was taken care of by Lynnfield; the removal of the need for a Northbridge at all. Once these two items were out of the way, Intel was free to move a small GPU onto the CPU packaging and use the available PCI-e Gen 2 lanes in the CPU Die for the connection. The rest is history as Intel can claim (and rightly so) that they have the world's first CPU+GPU offering.
Clarkdale puts together a Dual Core 32nm Lynnfield style CPU (complete with Hyper Threading) and a 45nm Intel Graphics Media Accelerator HD at either 733MHz (Core i5 6xx) or 900MHz (Core i5 6x1). This when combined with the H55, H57 or Q57 chipset would seem to make for an excellent entry level option.
Of course, there is more to Clarkdale than just this. Intel has made some adjustments to the smart cache, added in new hardware acceleration for AES algorithms and a few other "under the hood" advancements. Clarkdale also brings some old friends along with it, like Hyper-Threading, Turbo Boost and Smart Cache.
For the GMA HD, there are also some updates. Of course these are more for mainstream graphical performance and not gaming. They include optimizations for Silverlight and Flash, DXVA-HD Acceleration, optimizations for the most common HD codecs and advanced memory and power controls.