How many BlogSpot blogs?

How many blogs are there on BlogSpot? Google recently announced that in August 2009 Blogger will officially turn 10 years old. They're inviting users to send stories about what Blogger has meant to them over the past decade:

http://googleblog.blogspot.com/2009/06/blogger-is-turning-10.html

Their post includes four "fun facts" about Blogger but gives no indication of the number of active blogs, or even the overall number including lapsed blogs and invitation-only private blogs. The post talks of 'millions' of blogs on BlogSpot. Tens of millions? Hundreds of millions? Only Google knows for sure and they're not telling.

The second most popular hosted blog service, WordPress.com, posts user statistics each month. At the end of May 2009 there were 2,105,723 active blogs:

http://en.blog.wordpress.com/2009/06/15/may-wrap-up-2/

Is there any way to calculate the total number of blogs on Blogger? A Google search didn't turn up any reliable estimates. Can it be worked out from number of digits in the blogID? I don't think so. This blog has a 19-digit ID which leaves scope for an astronomical number of blogs — far in excess of the number that can possibly exist. Until sometime in November 2006 the blogID was an 8-digit incrementing counter. A little bit of searching showed it had reached at least 38 million before the new disguised IDs were introduced.

If you do your own research remember that some users set up a blog and leave it for months before publishing their first post. And if anyone has found a sure-fire way to work out the current count of Blogger blogs, please add a comment with the secret formula here:

http://pulsed.blogspot.com/2008/06/blogger-wordpress-debate.html