Last year around this time, I shared the download statistics of Drupal core so I figured that an update was in order. It looks like last year, from May 2006 to April 2007, Drupal core was downloaded more than 600,000 times.
These numbers do no include betas, release candidates or CVS checkouts. Also, we can't track downloads from mirrors, such as various Linux distributions, nor can we track installations through control panel software for hosting like cPanel or Plesk. Contributed themes or modules are not included in these numbers: we only looked at the main Drupal download.
— Dries Buytaert