Personally I feel like it takes away from family/friends time, even if that time is just standing in a line, if various people in the party have their nose in their ipads and such. Isn't that why most people go on vacation, to get away from emails and spend some quality time with their loved ones? I understand that it can be a good distraction for antsy kids, but what did people do before ipads came out. I'd be too worried it'd be stolen or get wet/dropped too...mine never left the hotel room.
This summer at WDW my family and I were at Rainforest Cafe chatting about our day while we waited for our food to arrive, and I happened to look over at the table next to us - the dad was playing on his phone, the two little kids were playing on ipads and one kid was playing his nintendo DS, and the mom looked bored out of her mind. I remember thinking it was such a shame they were missing out on a chance to enjoy each others company and the experience of the theme restaurant.