WordPress was born out of a desire for an elegant, well-architectured personal publishing system built on PHP and MySQL and licensed under the GPL. It is the official successor of b2/cafelog, as b2 development has stopped. We hope by focusing on web standards and user experience we can create a tool different from anything else out there.
It only took me about 5 minutes to get it running (transferring everything over from b2 was extremely simple) but there’s still a bunch of little tweaks I want to make. And, of course, I need to update the template.
If you are considering updating from b2 to WordPress, the only piece of advice I can give is to change $table_prefix in wp-config.php to b2. It eases the pain while WordPress tries to upgrade your database.