However today I discovered that I must have leant on it in the night as I discovered it in the bed with a slightly broken screen :( It now has a small part in the top left hand corner which is 'smudged' and a couple of lines down it.
It's still ok and usable but it's a bit disappointing - more so than a few crumpled pages of a paperback. I'll keep using it though.
(ps the book is Bulldog Drummond in case you're wondering)