Google.ca (Canada) is now PR7, I believe it was 8 last month. While that might be because of fewer quality inbound links I somehow doubt it and it can't be because of content, there isn't any.
A guess - they stretched the pagerank scale. It takes more links of equal value to achieve the same as fewer could before the update. Google.ca had enough pagerank value to equal 8 prior to the update but afterwards that same value is only worth a 7.
Potential impact, to internal links especially, is that our sites aren't propping themselves up in the same manner they were before the update, or more accurately the internal link structure doesn't have the same support strength.
Potential remedy: More. More content and more internal links. You can control those and internal links are the easiest to get. If you have several PR3 pages and link them to another PR3 page it can and does elevate to PR4 or PR5 in a future update, assuming they were relevant.
So, did Google stretch the scale? If so, could this be playing a huge role in the creature that is Panda? Just throwing more ideas and observations out there, if you can't disprove it you have to consider it.