I've got an FB account I use to keep in touch with family for photos, messaging, etc.
Myspace - never use it
Twitter - I use it when I need an answer about something, i.e., tweeting Xboxsupport
Linkedin - I have an account, I've yet to get anything out of it. I don't have time to "network" via Linkedin
Instagram - posted a few pics, mostly use it to post pics to facebook so family can see
I used to be heavily into social media in college because it was pretty much the best way to communicate with colleagues, but now I'm rarely on it.
I'll never understand those who constantly have to know what their friends are doing. It's like, live your damn life and stop worrying about others.