Jakob (a good friend of mine from the PHP UG Dortmund) has written a bash script to create class graphs (non UML conform, but what shalls?) from a PHP source directory. The resulting SVG is generated through GraphViz. He just ran the script on the eZ components. Here is a small excerpt:
Quite cool, I think, and it already helped us a lot to find inconsistencies in some other projects.
Read more on Jakobs blog (which I'm just adding to the Planet).