bears5122 - 6:08 am on Jul 28, 2010 (gmt 0)
I'm inclined to believe that if they don't get better with age, they certainly don't get much worse. I've seen far too many sites that haven't gotten any new links in awhile and still dominate the SERPs. I think the best evidence is to look at most results. You'll rarely find newer sites with fresh backlinks ranking over established sites with old links.
My guess is that a link doesn't reach it's full potential till maybe a year. It can help you, but not in it's fullest. Probably a way to combat text link purchasing. I think sites that haven't been getting links for awhile don't lose their stature, I just think other sites that are gaining links are getting stronger.