I also have a theory that its only for young sites. A lot of young sites are noticing PR changes in the last few weeks. The older sites are having nothing happen to there PR.
one of my site ganed from 1>3 and othor sites no changes even after backlinks are incresed but main url has no cahange from 2>2 . but some iner url got position from 0>1
Dont want to upset anyone, but PR update IS completed. And surmise about "young sites update" seems to be true. No Pr change for my old projects, while 3-month old site (with small amount af backlinks) managed to get PR4 from ground zero...
I lost my PR completely!!! It used to be PR5 then PR4 then 3 and now down to 0. One of my other sites has never gained any PR since I bought it. I don't know what is wrong!