For a long time, getting links to your site from others has been important.
At one time a few years ago, it was the whole SEO strategy for many, with "link farms" and link trading schemes all the rage.
Some people still seem to think that is what it is all about, whereas Google themselves freely admits it is not the biggest factor in rankings.
That doesn't mean it isn't important and it doesn't mean you should ignore it.
At the margins, it can be the difference between a number three rank for a key term, or a number one.
But effective link building is not easy, nor something you can accomplish overnight. And since it is responsible for only about 20% of your rankings, you certainly better not neglect other factors.
I think this article gives a decent perspective on the subject: How to Value Links?
We work with many clients in different industries, and with sites in different states of optimization. It is often many months into working on their SEO before it really comes up on our radar screen. Then it becomes something we just plug away at, month after month, and monitor for results.