What do you mean by “managing”? On my site there are 1500+ Blogs, but I don't have to manage a lot. I have set up categories for the blogs and move new blogs to the right one, if the blogger does not do that himself correctly. The blog owners can moderate their blog comments etc. themselves.
More of an issue are the categories of an individual blog, as many users create a new one for every entry.
And I like it that one user can have more than one blog.