I disable most notifications, and even the ones that are turned on are silent ones. I keep the phone aside on the table almost all the time, and consider myself a relatively mild user of the smartphone. Where I really miss the phone and feel handicapped without it is when I have to quickly look something up on google/dictionary. e.g, if I have a quick random question about why something is the way it is, what causes some symptoms etc. I can't imagine going back to childhood (90s) when we had to go to libraries or ask poorly knowledgeable people about stuff.
In a way, I feel this is the future. Human beings are supposed to become one with the machine at some point. People who dislike that or choose to stay away might actually be likely to be outcast and be considered weird. I already see that happening, for example when I tell people I don't have a facebook account. It boils down to, "Do I value personal privacy, or being connected to the world's information flow ecosystem?". And I am not sure that choosing to be private is the obvious right answer at this point. And it might not even be possible in the near future.