This page summarizes the usage of all projects on drupal.org. For each week beginning on the given date the figures show the number of sites that reported they are using (any version of) the project. Detailed usage information for each release of a project is available by clicking the project name.
These statistics are incomplete; only Drupal websites using the Update Status module are included in the data. As this module is now included with the download of Drupal since version 6.x, the data is heavily biased toward newer sites. Read more information about how these statistics are calculated.
This is the best and most up-to-date thread concerning CDN integration that I've found. The discussion contains a few examples of what others are doing for their projects.