I am wondering the same thing... I added a blog to my site to see how it works.  Created a couple test blogs.  Now I can't delete it.  I deleted the whole page.  Then if I add a new page and add a new blog module, all the old test blog stuff comes back.  is there any way to get rid of this?

EDIT:  I think I figured this out, although I technically only created one blog with child blogs since I can't figure out how to create multiple blogs!  :)  From the Blogs List drop down menu, click on Edit Blog Settings.  Scroll down and delete.  For some reason deleting the blog from other places doesn't seem to work, but from here it does.  I hope that works for you.  Unfortunately that would mean you have to do this for each individual blog.  I couldn't find a mass delete or anything.