Heh, every time I read a poll on the glass roof option for '09, all I ever see from Mustang enthusiasts is how hard the sky is falling. I think the biggest negatives on it are that it weighs 40-50 lbs, it looks best on black, it doesn't at least pop up in back, the rollout shade isn't 100%, and you're paying Ford to install it, and factory installation wages appear to be kinda high.
I don't know they didn't give it some sort of pop up moon roof mechanism at the very least. But then again, the glass panel on my old Scion tC would shake and wobble like hell at more than 40mph.
But it is an option, certainly won't be a long lived one, but nice to see it all the same.