Just a quick FYI that Google has just run the second 2011 PR update.

Something is going on with this update, massive shifts in PR have occurred on multiple of my domains that have been stable over the last 3-4 updates in 2010, additionally I don’t think that they have all been hit up yet.
Most of my domains received an increase including my online surveys domain, going up to a PR4 from PR0.

I believe the main thing that is holding the PR of my domains in place (or increasing them in many cases) would be the large number of high PR in content home page links that each of them have.
From a fairly quick observation, the old saying that “the PR of your site cannot exceed the PR of your highest in bound link” still remains true. After running an inbound link report on a couple of the domains that lost PR, I can see that they have dropped to the same level as the highest PR link pointing to them e.g. one of my PR6 domains that’s highest PR links is multiple PR5′s (including .gov links) has dropped to PR5. Same case applies on the domains I have seen increase.

I will post more on this later but for now go check your site out and see what the PR is. I would be interested to hear how your sites have moved and what you feel was the reason it shifted in either direction.