If a site's PR does not change during an update is it normal for traffic to decline during the update? (All of the DCs still reporting same PR) Does all the havoc caused by the update sometimes cause a temporary decrease in traffic?
Because PR is updated every moment of every day...a toolbar rollout means nothing to your SERPs. However, the google SERPs have been fluctuating, but I wouldn't have anything to do with your PR.
PR has nothing to do with rankings or traffic. PR only reflects the NUMBER of backlinks. But you might lose traffic because of an update which discredited some of your backlinks.