What should a fine social networking app have?

I am bored of Facebook, yes. Never knew how to use Twitter so that I do not fall asleep in 10 mins. Still, I have heard there have appeared new apps that buzz you when ppl you have selected pass by you. It is also curious to see their profiles (feeling like a spy) and know what they are about just before saying hi. Which apps would you advise? What should such app have so that you just love it?