Now Alexa measures traffic only if the toolbar is installed on the client. Its not a very good measure of absolute traffic, but its a great way to compare sites
Looking at this Joomla and Mambo CMS comparision, well, a picture tells a thousand words.
This was also interesting: Where do people go on joomla.org?
forum.joomla.org – 32%
joomla.org – 16%
developer.joomla.org – 15%
forge.joomla.org – 14%
extensions.joomla.org – 9%
demo.joomla.org – 7%
help.joomla.org – 5%
dev.joomla.org – 2%
Based on a thread at joomla.org, I put in some new numbers, I looked at both Alexa and some Google trends stats:
The first graph is Alexa traffic rankings. This bascially shows everyone that visited that site that had the Alexa toolbar installed. Its not very good for absolute measurements, but is great and relative ones. It shows that Joomla.org gets about double the traffic of Drupal and Mambo. All three of these had a big spike during April.
The second graph shows the (relative) number of searches at Google (www.google.com/trends). Again, it shows a clear (imho) dominance by Joomla.
One can only anticipate this growth increasing as 1.5 is released and the various press (hopefully) from the core team come into play.