A new Google PageRank update is underway. PageRank is a number that signifies something about the importance of a page to Google (based on the pages linking to it) that can be seen with a Google Toolbar. The PageRank is not the most important factor in search results but it is an easy view to how important a page is so is some webmasters find it interesting. I have seen many pages rise in PageRank but also some fall by one point - noticing falling PageRank seems more common this time around.
The displayed PageRank is updated perhaps every two months. Google uses live data in determining search results, so you finally seeing the updated PageRank should not effect how your site fairs in search results. PageRank follows a logarithmic scale (so, for example, a 6 PageRank is 10 times greater than a PageRank 5 - of course really it can be from just a tiny bit better [just "over the line" that separates 6 from 5] to almost 100 times greater.