I do not understand well the meaning of the bar of the pagerank distribution in the webmaster tools. Sometimes the "low pr" bar fills up, now for example it is emptied of a piece and that has filled a piece of the "not yet allocated" bar (i have the impression that this is not a good sign). I'm a bit confused, someone can give me the correct meaning of this? Thanks
Personally I do not find the PR distribution report very useful. It may be more useful for a large website that is concerned about getting their PR spread out evenly across their entire website. I believe the bars represent the percentage of your pages that fall within that PR range. It is not a bad sign that some of your pages do not have PR allocated yet. This is likely because those pages are just too new.
All I can say is that I find the bar confusing too. Sometimes it's nearly full and not at others. It doesn't seem to have any effect on the traffic to my site though.