I have no problem with it.
I think people who do it should have their moviegoing privileges taken away.
I think it's less annoying than the guy next to you loudly munching on his popcorn or crinkling cellophane.
It doesn't make a difference to me, but I do think it's kinda nutty to pay for a movie, then stare at a tiny screen most of the time instead.
It's not the kind of thing I notice.