robdwoods - 5:35 pm on Jul 29, 2010 (gmt 0)
My data on this is more anecdotal than specific but from what I've seen on my sites, there is an initial boost from a fresh link, particularly when that link comes from a "social" source. Social sources seem to have a greater "freshness" weighting than more static sites. Links in content areas of pages more stable than social sites seem to need to age a bit. My impression is that they can take a couple of months to start passing some real value and several more to pass their full value. I think they age more like a white wine than a red. It takes a while to reach their full potential but at some point, all other factors about the linking page being equal, the potential levels out and stops increasing. Again, these are my impressions from doing numerous waves of link building and assessing the results but I have no hard data to definitively back up my interpretation.