How Many Blogs?

Everywhere I go I see links to blogs and announcements for new ones.  All of the blogs are by the same author.  I find myself wondering, why and how?

I realize that there are many different hosting sites out there. There may be a chance that you can find some new readers by visiting the different sites.  What I guess I don't understand, is why do you start another blog through that hosting site.  I believe you may have to sign up, but is it a requirement to start and entirely new blog?

The how is simply a time management issue.  I can understand having one or two blog without any problems.  I have seen some individuals who have three (a little shaky), four (okay starting to freak out a little), and even five or more (I have gone completely insane and no longer have a life).  They don't simply copy and paste between their blogs either.  Each is an independent posting.  I have trouble keeping up with one blog and networking sites. 

So I ask, how many blogs are to many to keep up with and still maintain your sanity?