Key differences between the two 'major' sockets for intel's core i7 products at the moment...
z68 is the chipset that uses 1155 socket.
This is for your i5 2500/k to your 2600/2700k i7's.
Z68 offers a split x16 pci-e bandwidth lane as its native from the processor. This means the Z68 platform is great for 1-2 GPU's and Sata6 of which it generally comes with a native intel controller which is far better than the more available jmicron/marvell controllers used for sata6 on older chipsets.
Socket 1155 cpu's ALL feature on-die GPU which is an intel gpu on the cpu.
ALL OF THEM.
For average use, and some hardcore gaming a slightly overclocked 2500k with a decent gpu like a 580 or a 7950 will net you best bang for buck. 2600k or 2700 for the best will reduce the need to OC the cpu as much and net you a marginal difference in cpu intensive apps. Loading a z68 chipset up with more than 2 graphics cards is overkill for the platform
Thats where 2011 and the x79 steps in. 2011 socket Cpu's do not have an onboard GPU like the 1155 socket cpu's, instead they have an additional 2 cores. x79 is perhaps the direct replacement for 1366/i7's of the first generation as they are designed with the idea to be a mainstation, as the cpu and the gpu are again seperate. x79 also requires quad channel memory, z68 only requires dual channel ddr3.
So when deciding on what you are after have a look at it this way, 2011 is a larger buy-in, but having said that, as a hex-core owner, cpu power is always necessary so its a bit more future proof for the moment, but word is that a decent z68 motherboard is ivy bridge compatible, but you will have to wait for them to drop....
so, what will you use it for and how much are you wanting to spend for what kind of performance?
Nolite te bastardes carborundorum