I've never seen this in real life, but apparently some priests put everything they need to read during a mass (gospel, prayers, homily) on an iPad.
The priests they mention in the article are in Europe. It makes it easier for the priest to keep everything together, no paper flying around, no heavy book to carry up to the alter.
One person at the Vatican, however, wants everyone to stay with paper books:
" Father Antonio Spadaro, known as the Vatican’s “cyber theologian,” said that devices such as iPads, smart phones and tablets should not be used instead of missalettes at Mass."
I dunno. I think in the long run electronic devices will be employed in churches. A hundred years from now, will anyone even remember books existed?