Google is doing it with automation Dave, your reputation is part of the score or input just like Page Rank is a part of the algo.
I run a small blog network and it is filled with spam (I try to delete them as fast as spammers make them, but like Blogger is filled with splogs.....) as "so called
SEO's" make blogs with tons of links pointing to their pages, this sort of thing is out of control, Google only indexes a small percentage of these "Blogs", the rest are moved to the invisible supplemental index. Maybe the solution is to create a blog network with "no follow" as default !!!
I wrote one blog on the network and Google indexed it simply because it was not filled with outgoing links and it was original content, but I can tell you that 98% of the blogs on that free blog network will never see the light of day because of the way people put them up.