If Sarah runs for the GOP nomination then she will win, but everybody she beats would have stood a better chance of beating Obama.
I gather this is based on the assumption that liberals would rather have babies than have a President Palin and would vote in droves. I would say that if the GOP tried another McCain, with an equally irrelevant running mate, then conservatives won't bother to vote and Obama would win at any rate.
Of course, Sarah would be doing her best to GOTV and will ultimately be blamed for the loss. So I say screw them all, Run Sarah Run !