Larry Garfield has posted the results of some of his research into popular PHP frameworks and projects and see how they handle their structure as it relates to the PSR-0 standard.
As Drupal is in the process of considering how to restructure code to best leverage the PSR-0 standard, I figured it would be wise to take a quick survey of how some other major projects organize their code bases. This is not a complete rundown of every project, simply roughly comparable notes for those areas Drupal is currently discussing. I am posting it here in the hopes that it will be useful to more than just Drupal.
The projects he looked to for his examples were: