I have, more times than I can remember, looked up restaurant recommendations, reached consensus with other people wirelessly, and then made a reservation, all without leaving my smartphone, while standing on the sidewalk somewhere.
I have also walked up to a restaurant only to find it closed, and found a delicious alternative within seconds thanks to Yelp, Urbanspoon, et al.
I have taken pictures, uploaded them to [social network] and received responses within minutes, if not seconds. I have met up with friends because the GPS told us we were near each other.
My smartphone is great for consuming the day's news (especially on a high-ppi screen, reading is a joy) while on the train to work. Laptop or even tablet? Don't be ridiculous, I need one hand hanging onto a railing.
My smartphone is also my light meter, when I'm out and about playing with vintage cameras that pre-date my birth. Not a very typical use case, but one where a laptop or even a tablet would be utterly useless.
I love my smartphone.