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?
Yeah, I don't know about every month but I always carry a microfiber cloth in my back pocket, and I'll rotate them and just run through the wash if they've been in use for a bit.