This blog is written using WordPress which is a branch of B2 and is about to become the primary distribution of b2/Cafelog. I have been using b2 for some time now and have really liked the flexibility of the code and the simplicity of the coding practices. Some of the features of b2/Wordpress that I really like a lot are:
Simplicity of installation and configuration
The ability to login through the blog itself and post on the fly
Simple template design with WELL documented functions and code patterns
Very faithful user base with extremely helpful forums
Proliferation in the Blogosphere, which means faster hacks and bugfixes
Willingness of people to maintain the code even after the original author loses interest
Last but not the least, powerful (albeit expected) features such as teams, multiple post options, built in comments, track and pingbacks, email posts etc.
Cafelog runs relatively efficiently on my server without being too much of a resource hog. I use my blog extensively and hope to keep publishing with b2 and WordPress for a long time.