Every time a Page rank updates, the same common issues arise, creating confusion regarding your web site's Page Rank. What the Page Rank and its fluctuations mean cause confusion to the site's owner. Some usual themes are the following:
1. If, during an update, your PR goes down, it is not necessarily a penalty. The PR is found in the Google toolbar, and is simply the grade that Google assigns your site. Losing powerful links or if a site that links to your site loses PR, will result in your PR lowering. If Google alters changes the way they determine PR, you can also lose PR. Keeping your content fresh will ensure your PR remaining steady. There are a lot of reasons for PR lowering, but none of them are penalty related. Being penalized will only occur if you disobey Webmaster Guidelines, and you will see that penalty in removal from the index or drastic drops in rankings.
2. PR that is displayed is not current. The PR is only current after an update. You could have made a well rounded link profile, even added an interface for user generated content, and still have a PR4 after a couple months. Do not worry about it, because you do not know your actual PR.
3. Higher PR does not mean higher rankings. Instead of focusing on the PR, focus on your traffic, rankings and conversions. Tons of searches with PR0-3 outrank PR4-6's, this is proof that PR is not the sole measure in Google's algorithm in determining your site's parking spot. Do not worry about your PR, unless you are selling links and need to show your PR is high. Do not ignore PR, but keep it in perspective. PR is the generic snapshot of your site in Google's eyes. You will usually have a higher rank with a high PR, but that is but one puzzle piece.
4. PR juice flows. Without obsessing about your PR, understand that acquiring high PR links will flow PR to your site as well. Worrying about your own site's PR may not be as valuable as making sure that your incoming links are from high or mid PR sites. If you are working towards obtaining links, high PR pages mixed in, naturally, will greatly benefit you. If you look at PR as a trust snapshot, then obtaining a link from a more trusted site, at the same time being relevant to your industry, will not only boost your PR, but your ranking as well.
In general, a rise or fall in PR that doesn't coincide with search results or traffic, should be of no worry. While it is great to follow your PR as it rises, what really matters is Traffic.