Kevin over at TailRank has put up a graph showing the cyclical nature of story volume from TailRank's POV. The graph shows the number of stories per day that TailRank ingests - that is to say, the number of threads that it considers when creating its real-time view of the blogosphere. Typically, TailRank's home page shows 30 such stories. TailRank appears to be looking at something like 6k stories on a typical week day. If we guess that there are 5 links per story (the head is going to have many more, but the long tail will lower the average number) then TailRank would be considering something around 30k posts per day. This is, however, the number of posts involved in a thread. TailRank will actually be crawling many more (though I'm guessing that it works with a moderated blog list - that is to say it doesn't crawl any old blog out there).