Google has updated the page ranks displayed in the google toolbar recently. Many webmasters have reported a drop in PR, with some sites dropping back down to 0.

Googles reponse on the issue is that Page Rank is just one of 200 measures of ranking algorithm, and the size of your green bar in the toolbar should not be a concern.

This page rank update comes shortly after a major ranking algorithm update. The ranking update did far more to affect websites traffic and rankings than the PR update did.

The PR indicator in your google toolbar is actually only a minor measure of your site's ranking, and for a true measure, you should use web metrics or google analytics to establish your sites current profile in the search engines.  If you have a high PR then its more likely you will have higher traffic, but not guarenteed. For example. this site currently has a PR of 4, and gets far less traffic that some other SEO enabled websites that I monitor which have a PR of 3.