WordPress is scaling new heights! For those who came in late, WordPress is the best blogging platform and it open source.
You can either use their free blog service at wordpress.com or download WordPress and setup your blog on your own domain.
WordPress Vital Stats:
WordPress 2.9: 10.3 Million Downloads
WordPress 3.0: The recently released version has already reached 3 Million downloads.
Number of WordPress Plugins: 10,000
WordPress Plugins downloaded: 100 Million
Google Search results: 202 Million results
Now those are huge numbers for a software which is primarily hosted and is not a client application.