A Survey of 2,368 Drupal Sites
Back in May of 2008, I did a survey of 1,370 Drupal sites, and came up with some interesting version statistics. At the time, Drupal 6 had been out for about 3 months, and the adoption rate was still fairly low.
It's been 2 years now since Drupal 6.0 was released, and I thought it would be interesting to revisit the numbers. So, here's a fresh survey of 2,368 Drupal sites:

And here are the numbers from back in 2008:

If you're interested in how I came up with these numbers, you can read more about the methodology in my original 2008 article.
So, what does it all mean?
Drupal 6 has certainly gained a lot of popularity in the last 2 years, taking a healthy lead over Drupal 5 in raw numbers. Taking a deeper look, however, it appears that most of Drupal 6's growth comes from new sites. Upgrading does not appear to be a priority for most Drupal 5 sites, and even Drupal 4.x still held on to almost half its audience, despite being unsupported since 2007.
Clearly, Drupal's painful upgrade process has been a major factor holding back the adoption of newer versions, and for many webmasters, Drupal 6 just didn't provide enough to make upgrading worth it.
In the end, Drupal 5 is still "good enough" for most, and barring any major security problems, we'll likely see it stick around for years to come.

