MariaDB just released MariaDB 5.1.50. Linux, Solaris and Windows (32-bit) are supported. Go give it a twirl.
Its also worth noting that today when you go install Drupal, and check out the documentation for requirements, you’ll see that MariaDB is now a recommended option.
Via the new news page at Monty Program’s newly designed website, I also found out that MariaDB is now recommended in the documentation for the next release of the Zend Framework. See the changelog.