If you came by our church you'd see that about 2/3 of the folks are using mobile devices or tablets.
When we preach and teach, we prefer to use a physical copy along with whatever our notes might be on. Works better for us all.
I don't generally have a problem with it as I can talk about another passage and people can go to it easily. Sure, some are checking FB or email or texting, but that's gonna happen anyways. We can say something about it, but that doesn't change anything.
When I've been teaching in smaller settings I usually joke about people checking email, texting stuff, or playing Words with Friends (or whatever new game is hot this week) and it gets laughs...and people who look at their spouses with "that look."
We've tried to leverage this for our services by having interactive elements. We ask people to post on FB or Twitter something they've heard today. Maybe retwteet our big idea. Also, we use a polling software that let's us take realtime polls from the crowd via text message.
It is all in how you leverage it. Just a thought.