Drupal 5 vs Drupal 6 module usage
When the usage statistics page for Drupal contributions was released recently, I was pleasantly surprised to see how many people were using the Availability Calendars module, and amazed at the difference the Drupal 6 release had on the usage figures. The graph below shows that the usage was quite steady on the Drupal 5 release, but when the version for Drupal 6 was released, it massively boosted the figures.
So, if you are the maintainer of a Drupal module or theme, and haven't yet released a Drupal 6 version, it looks like you're really missing out on potential users.
Comments
Data is skewed from how it's collected
The only usage reporting from D5 are sites running the update_status contrib module. In D6, update.module is in core, so a higher % of D6 sites are checking for updates and therefore providing usage statistics. See http://drupal.org/node/327548 for the effort to clear up the help text on those pages to explain why the numbers lean towards D6.

