H67 boards can use the CPU's integrated graphics. They can also improve the graphics performance by overclocking that part of the chip. They cannot overclock the CPU cores though.
P67 boards cannot use the CPU's integrated graphics. However, they can overclock an unlocked CPU (2500K/2600K) to its fullest.
Quick Sync accelerates some encoding/decoding/transcoding functions. It's part of the CPU hardware, but also requires the program to be written specifically to take advantage of it. So far, only certain programs are, but others are likely in the process of re-coding.
Z68 and Virtu allow the system to switch on the fly between a discrete graphics card for gaming and the integrated graphics with Quick Sync for those who need it. Z68 can also overclock the integrated graphics as well as the CPU cores. In that way, it's a combo of H67 and P67.