Though my vikuiti is unscratched, I can clearly see a difference where the stylus has been used most of the time (on the right scroll bar and on the virtual keyboard), and that's after less than 2 months of use.
Cleaning it energically will remove the spots for a while, but they're back in no time.
Maybe because of the piss-poor performance of the touch screen (especially when you're trying to right click a link in microb) I'm going too hard on it.