Here's a fun trick that just came to me. By installing PolkaDot into one of its own subdirectories, you can have a standalone blog whose posts also get incorporated into the main blog. Here's an example. This blog has a category for Tea. By placing the PolkaDot installation files into the "Tea" directory, I can also have a separate Tea Blog.
The posts that show up on the standalone "Tea Blog" are exactly the same ones as show up in the "Tea" category for the main blog. Note that if you make sub-directories under Tea, those will show up on the Tea Blog in a category with the same name as the sub-directory, but not in the main blog. PolkaDot only goes down one level when building categories.
So I could make "Green Tea" and "Black Tea" categories, but posts in those categories would only show up in the Tea Blog. Only posts to the "Main" category on the Tea Blog would also show up on the main blog.
I'm not sure, off-hand, of a good application for this feature. But it is a way to have multiple blogs, each with their own look and feel, while still being able to aggregate them together into one single blog.