We all know that PR comprises of backlinks to a particular page or PR passes on from High Page. We also know that Google or any other Search Engine suggests to block a page by using the username and password.
If that is the case then how come we see PR for Gmail inner pages or PR for Orkut pages when logged in?
In reality the PR should never pass to the email account pages when you have logged in.
The PageRank shown in the Google Toolbar is not an accurate measure of a page’s true PR. The Toolbar PR is usually updated 4 – 6 times a year (sometimes more, sometimes less depending on algorithm changes and other search updates).
As a result of this, there are a lot of pages that will show no rank for months, which really do have a ranking hidden to the general user. Or the complete opposite where pages within a well trusted domain like Google (even non-indexed, password protected pages) will show PR that doesn’t exist.
In these cases it’s nothing more than a glitch in the Toolbar as it’s attempting to guesstimate what the PR would be based on the value normally passed down from the root domain.
You can still use the Toolbar PR as a rough guide, but for the reasons above, it’s best not to focus primarily on the Toolbar PR and use other metrics to measure the true value of a page.
Hope this helps.