GWT offers the option to remove single urls and entire sections of a site from the internet. Here's a simple experiment that sheds a little light on how Google works.
- request a removal of an entire directory, traffic will fall accordingly.
- later restore the content but don't undo the completed removal, traffic will fall some more
- undo the removal in GWT and traffic will bounce back with a vengeance.
That second part is what I find interesting. Adding content to a section of your site that is blocked via GWT somehow causes a loss of rankings, the more content you add to the blocked directory the more you lose traffic to the entire site.
It makes sense in a way, you're bleeding pagerank into parts of a site Google can't follow anymore but still I can't help but think this might help some Panda victims who are busy trashing large sections of their sites right now.
It's apparently not enough to continuously add fresh content, you can improve rankings by pumping up existing content. I think that's something to think about when setting up a new website. You might be wise to choose a list of keywords you need to rank for and create a page for each and then add content to those pages on an ongoing basis. Turn "a post a day" into "a posts worth of data added to existing articles" and you may be rewarded. There isn't strength in numbers with Google, there's strength in rankable quality.
Of course I may also be reading too much into Google behavior, it happens :D
note: I noticed GWT no longer tells you what % of your site has low PR, medium PR and high PR anymore, they did once upon a time I think.