sunroof on current car (had for 4 years, I never close the blind and I've not had any problems with seats etc). Gone for one again for the Mk6 on order (does let in a lot more night, especially on Mk6 with the dark tinted rear windows (thinking of the little one in the back more than anything).
But as one of the other guys said, if you're worried, just close the blind = problem solved.