Googler, John Mueller, said in a Google Webmaster Help thread that Google Toolbar PageRank will not change how Google crawls, indexes or ranks your web site.
This is just one more confirmation from a Googler that Google Toolbar PageRank should not be obsessed over by webmasters and SEOs.
Google's JohnMu said in response to a novice SEO:
We do Toolbar PageRank updates 3-4x/year but to be honest, it's not something that you need to wait for. The PageRank shown in the Toolbar is an older snapshot of the PageRank that we use internally (which is continuously updated). Changes in Toolbar PageRank will not change anything with your site's crawling, indexing, or ranking, so as a webmaster, I'd strongly recommend focusing on something else.
For most SEOs, this is nothing new, but a lot of novice SEOs need this reminder. It is always good to provide this reminder from Google directly, so now you have something to point your clients and novice SEOs to, once again.
Forum discussion at Google Webmaster Help.