Based on the data from Builtwith, which is as recent as 3rd Oct 2011, WordPress now powers 61.46% site in top one million sites, way more then both Joomla and Drupal.
cms _distribution_Oct_2011
When the sample was reduced to top 100,000 sites even the WordPress share was whooping 54.07%.
cms _distribution_Oct_2011_a
Even for top 10,000 sites, WordPress accounted for 49.72% Sites.
cms _distribution_Oct_2011_b

Some neat stats isn’t?