PR export to the toolbar has nothing to do with serp changes. Matt Cutts explains algorithm updates and data refreshes Algorithm update: Typically yields changes in the search results on the larger end of the spectrum. Algorithms can change at any time, but noticeable changes tend to be less frequent. Data refresh: When data is refreshed within an existing algorithm. Changes are typically toward the less-impactful end of the spectrum, and are often so small that people don’t even notice. One of the smallest types of data refreshes is an: Index update or data push: When new indexing data is pushed out to data centers. Google refreshes some of its index pretty much every day, which generates a much smaller day-to-day change that some people call everflux. http://www.mattcutts.com/blog/explaining-algorithm-updates-and-data-refreshes/