I have never bothered too much with link building apart from a little blog commenting, occasionally submitting a blog post to a few social media sites and a touch of Yahoo Answers once in a while. This has brought in a small amount of traffic for the sites that I have done this for but nothing spectacular.
The thing is, the very first website I ever made has generally been at #1 in Google for well over a year now. This site has only 146 external links which have occurred naturally over time just like big G wants. One thing the site has is lots of good content (not all unique either) and a large number of internal links (2735).
I have done hardly any link building for this particular site but I did get some very good reciprocal links from other sites in that niche, who asked for them because they recognised a decent site when they saw it.
I have even had requests from magazines and TV people to see if I could find some of my visitors for them to interview so I guess they see it as a bit of an authority site, which is quite funny really as I only created it to sell affiliate products.
What I am saying is that a quality site in a particular niche doesn't need thousands of back links to succeed.