Maybe somebody else have already addressed this question but I just want to ask this in a way that it will clear my confusion. Why does email (gmail) has a high pr even int the compose page? Does this means it also getting many backlinks and people are linking to them?
Why does this matter? The obvious explanation is that the interior pages have more links pointing at them then the main site does. www.example.com could have pr5 but if the www.example.com/interiorpage1.html has more links that page will have a high PR. I've said it once and I'll say it until I'm blue in the face, don't worry about Pagerank. Be more concerned with quality content and relevant natural links, those two factors will get your site top listings in the search engines, regardless of the pagerank.
Thanks for the explanation SCLocal. I wondered if it is enough for internal linking that in a compose page of gmail possess a pr8. But then again the answer for this would be you explanation. And also thanks for the side advice. What might Google Caffeine has to offer site ranking. I'm getting nervous.