For us crunchers, i don't see the real need to get the Z68. But maybe your sis would get more use out of it than we would.
It doesn't support anymore PCIe lanes than the H/P67 does. Sure, you can switch between integrated graphics and a GPU, but at the cost of running your chip hotter, limiting your overclocking abilities. Caching frequently used data on an SSD? Why wouldn't you have your frequently used data on the SSD in the first place? lol Hell i don't even have an SSD so again, that's useless.
However, the Z68 does offer some overclocking ability that the H/P67s don't. But isn't that what the BIOS is for? Except that you can overclock CPUs that have locked multipliers (though it's very limited), i don't personally have a need for the Z68. But we're all different
PC Magazine Z68 article