I don't think the update was right, or else they have changed how the PR is calculated.
One of my sites,
www.commondirectory.com went to PR5 from PR0, it has only been up a few months.
Another directory,
www.alldotnet.com stayed at PR4, but it has been online 14 months and has a lot more pages indexed and backlinks.
I saw a lot of people saying they have sites up a few weeks that also went to PR6 and they have next to no content/backlinks.
There are a lot that are right, but I think some are wrong, including my CommonDirectory PR.