tedster - 4:19 am on Jan 22, 2009 (gmt 0)

There's a related comment from Matt Cutts:

We're pushing PageRank canonicalization updates (as opposed to PageRank values) much more regularly these days, so my first response in a situation like this is to say "Don't Panic," especially if your site hasn't been selling any links that pass PageRank. Normally new canonicalization maps are pushed a few days later and that will often resolve things. For example, a large retail website had a PageRank go from 7 to 0 recently, but it was because of a deep url/canonicalization issue with their home page. Within a few days, the system had selected the canonical url that most folks would expect and the PageRank came back without anything done by a Googler. [seroundtable.com...]

Hmmm.... PR canonicalization updates following on the heels of a toolbar update. That does clarify a few things we've noticed over the past few PR updates.