In this round of PR update, here is the broad Consensus:

1) Sites that have existed for some time now have commonly seen their home page PR reduce (new sites are the exception as they have commonly shot up. My SEO blog went from PR0 to PR5)

2) There seems to be a somewhat different way in which PR is being calculated.

There are of course many more points being speculated, but these are the 2 that seem quite widely believed and I personally do buy them.