tedster - 5:02 am on Dec 28, 2007 (gmt 0)

There are some mentions in Google patents about backlinks getting stagnant and not growing - and that kind of staleness or stagnation might cause a demotion in rankings, according to those patents at least. It's possible that this factor is actually in play, but it would be a rather subtle factor, and not a cause of total vanishing or disappearing.