Social media sites should not be overlooked as a good opportunity for carrying out link building. Whether you're on the major sites, or more specific, niche sites for your blog/website, whatever you mix, there is link building potential everywhere you sign up.
My theory, and practice is to use these sites to network with people in your niche, more specifically people who run the websites you would like a link from. I don't do this in a fraudulent way myself. I'm a nice guy, honestly! When I do this for my own personal site, or the company's site, I am genuinely trying to build long-lasting relationships, preferably beneficial to both parties.
One good reason for making these a genuine relationship is because building links this way are a timely task. Rarely is this pulled off in a few tweets. Those that you are able to build links from quickly sound like the ones who may be a generous link giver (which goes against the tougher to build links are the better links theory... a theory that I haven't written down, so you may not be familiar with. Well done Barrie.). Or you're very good with goods.
If you blog about something you're passionate about then this theory won't be a choir for you. In fact, I believe this will be one of the more fun link building theories for you. Be personal, give them something of value, do whatever is required to get talking with your targets.
So sign up to Facebook, Twitter, LinkedIn and all the other social media platforms out there and start networking today! Enjoy.
PS - To all of my 276 followers on Twitter - this does not mean I am only after a link from you! Only some of you ;)