Recently I watched a video of Matt Cutts and there he mentioned that they are now keeping an eye on social signals as well. So should I also get some back links from social media/networking sites ? I also would like to know how social signals affect SEO ?
That is a very old video you are referring to. Social impact is already very deep now. Get yourself updated.
I'm a big believer in the increasing role of social signals in search. Likes, +1s, and social links are still a noisy signal, which affects their use by search.. thanks...