Google has one of the most active robots in the industry.
Most people don't know that Google does index each web page individualy and has PR value for each page.
When a page is indexed it is store in Google cache.
The easiest way to see your web site Google cache is by typing the full URL without the
http://www. into the Google tool bar and see if Google display a list of resources found about your site. Here is an example of what you see when I search for Cnn.com:
CNN - Cable News NetworkIncludes US and international stories and analysis, weather, video clips, and program schedule.
www.cnn.com/
Google can show you the following information for this URL:
Show Google's cache of cnn.com
Find web pages that are similar to cnn.com
Find web pages that link to cnn.com
Find web pages from the site cnn.com
Find web pages that contain the term "cnn.com"
Click on the first option Show Google's cache of cnn.com... then on that page you can see the date and time the robot has indexed this page. I believe the PR ranking occurs shortly or perhaps at the same time this index occurs. Only the PR value not the visible PR value on your Google toolbar.
Hope that helps a bit...