Meh, for the most part I like staying engaged with work and the interesting people I know... not so much with some random person next to me in a public place. You can have as much or as little competing for your attention as you want, so if you don't like someone checking their phone or whatever, maybe you should be more interesting.
Seriously though, I'm not one to randomly check FB or CP while I'm talking with someone and I'll ignore texts if I'm out with people unless there's an appropriate time to do so.... but, the whole "missing out on life" just seems odd to me, like when someone goes into a BB thread during FB season and is all "omg, you're talking about BB!" like football takes 100% of our attention for 5 months.
It's nice to disengage from it all every once in a while though. I've noticed those who were the slowest to get a smartphone in fear of being available 24/7 seem to get the most annoyed when I ignore a text for a few hours.