I have a smartphone (iphone) and use it for many reason, social networking not included.
- Phone (duh :bleh

- Lots of texts, and easier to text with a full keyboard (physical or touch)
- internet, never know when you need to find out something on the go!
- email, part of internet bit
- GPS, never get lost
- its an mp3 player too!
- apps of all sorts are a bonus (info, online banking, news, weather, etc...)
- functions as my alarm clock (different times for different days, absolutely LOVE this feature)
- Syncs automatically with my Google contact list and calendar
- In the case of blackberries, BBM, very... erm... nifty
I dont exactly check facebook whatsoever, but if i do get a notification, it updates me nonetheless, so im losing nothing.
All this means to me is convenience, I don't have to be at a computer to perform petty tasks like checking for an email I've been expecting or finding the location/phone number of a store of some sort. I appreciate smartphones for that.
A lot i know, only have a smartphone to text and make calls (texting mostly really..) and they find the usability of full keyboards are very good for that. I'm surprised to see so many pay for data plans and almost never use it, at least im happy to say i take full advantage of my data plan.
The plans used to cost a lot, but its getting better. A plan i used to get a year ago which costed me $90-100 now costs me $60 and I'm getting more out of it, so its slowly dropping.