Lens manufacturers say that anything other than a microfiber cloth will damage the coatings on a lens. But microfiber cloths eventually pick up crap and they look like they're a pain to wash.
How do you keep your lenses clean? Are you using cloth/kleenex or microfiber cloths? If you use microfiber cloths, how do you clean those?
I just clean the lenses of my glasses with my cotton t-shirt. I need to clean my glasses twice a day because they get foggy due to my oily skin and oily eyelashes. I have not noticed any scratches yet (I have been using these glasses for around 5-6 years). However, I used glass lenses and not plastic lenses. The plastic ones scratch easily.