londrum - 1:32 pm on Aug 13, 2012 (gmt 0)
maybe its got something to do with all the social signals. how often do they update that info? would they really be able to do it on the fly?
maybe each site has an underlying score, with remains fairly constant, and they factor in all the social signals every month, or whatever it is. that is when your site drops down (probably because other sites have got much stronger social signals). but social signals are no good if they are not fresh, so they pay less attention to them as the weeks go by. thats when your site slowly recovers its position, based in its underlying score.
and then when the next month comes around, they factor in some fresh social signals, and the whole thing repeats. obviously im just guessing.