Do you use any apps?
Thats a good question, and I'm going to assume it wasn't being sarcastic.
A few months ago, I was at my girlfriend's parents for the weekend visiting. Her mother wanted my number and I gave it to her, she entered it into her android phone and then text me to confirm the number was mine and so I could add the number to my contacts list. At the time my girlfriend was reading a book on my Windows Phone and she saw the message pop up, and was trying to reply back.
Firstly, when I told her mum my phone already had her number and contact information and there was no need to add her number from the sms she was confused. I had to explain that the contact details she provided on her facebook profile were being used. Next, when my girlfriend didn't want to text her mum back due to sms charges (being in the same room lol). she was prompty told by her mum to load up the windows live or facebook app to do so, and it'd be free as we were connected to the wifi network... this again confused them when I had to tell them facebook and windows live messenger was build in to the messages and there isn't a need for the "there's an app for that" mentality anymore.
Its just little things like that, where we don't need an extra app for something that is the same thing just different platforms. Apple coined the term there's an app for that and people have brought into that idea of how smart phones should be for far too long.. and I mean that in the sense that you don't need an app to see somethings, sometimes you can do with a live tile and that itself is a hole different topic
but yeah, to answer your original question.. I use a few apps, but the features most people use their smartphones for,. they're built in to the OS. The rest... if you manage to sort out the boob and fart machine apps, there are some good nuggets that are actually useful for non-generic things.