A few months back I posted about our latest whiteboard and I thought I'd report back with an update. Initially it seemed to work very well, the markers wiped off easily with a nice soft cloth. Then it started to get more difficult, requiring more friction than should be necessary. Our first thought was that we had finally worked our way through some film that had been applied to the plexiglass, but then the next week it seemed to be fine again? Our guess is either something about the humidity, or the makeup of the individual markers determines how hard it is to remove.
But the answer finally appeared - Magic Erasers remove the ink with no effort, and they are soft enough not to scratch up the plexiglass. Interesting stuff on the eraser part, worth following the link!