Fingernails on a chalkboard has never bothered me. Neither does rubbing a balloon. I wonder what the criteria for having or not having the negative physical reaction they describe is.
whoever57 writes "According to Prof Kubiatowicz from Berkeley, each time an additional book is downloaded to an e-reader, the mass of the e-reader increases. The effect doesn't really make the devices more difficult to carry: the professor calculates that 4GB of books would increase its weight by a billionth of a billionth of a gram— about the mass of a single virus or DNA molecule."