For those that have older tops or just like to roll them up instead of unzipping them (on tops that even allow that), rolling a soft towel up inside them is a good way to help them stay more scratch-free (if there is such a thing) when rolled up.
I always get some inexpensive large terry-cloth bath towels in a color that closely matches my vehicle and keep them folded up in the corner for when I want to either roll them up or fold the top down.
The soft material can also be used as a gentle dust wiper if you're careful, which prolongs the clarity of the windows even further. Rolling up dusty windows isn't exactly good for their health.
Attaching some velcro to the top and the towels will even let you keep them attached when the vehicle is parked or stored. This keeps excess dust, bird poop if outside, and sunlight off the windows. Good for lengthening the life of the windows AND for privacy when camping.
Privacy isn't such a big thing to most, but if you sleep in your rig or have more shy members of the family, this can come in very handy.
And just keeping dust and sun off the windows can be a HUGE thing in itself!
Paul