deadsea - 3:47 pm on Oct 21, 2011 (gmt 0)
In my experience, the links that you are building now start to really pay off in about a year. After a year of link building you can look at the pages that you built links to vs the pages that you didn't and see a measurable difference in the amount of traffic coming in. If you have two similar sites, one of which you built links to, you can start to measure the differences in about 6 months. In a year, the site with a great link building campaign should be flying high compared to the one without.
The other thing to keep in mind is that Google appears to be moving away from links as their sole source of "recommendations". It sounds like you are doing it, but link building without a social campaign doesn't make sense to me these days. If you are a merchant, make sure you are getting good reviews from your customers on shopping aggregation sites.
SEO used to be about keyword targeting and links. Now its quality content (including keyword targeting), recommendations (including links), and user satisfaction.