On the SquizLabs site they've shares the results of their coding conventions analysis of PHP projects using the PHP_CodeSniffer tool.

PHP_CodeSniffer, using a custom coding standard and report, was used to record various coding conventions across 193 PHP projects.

They've broken it down by the list of rules included in the default coding standards including:

• Array end comma
• Class defined in namespace
• Function has doc comment
• Adjacent assignments aligned
• CamelCase method name
• Line length
• Spacing before object operator

Each item on the list has the current measurements represented as graphs and a historical view about its previous usage. You can also view per-project statistics for a wide range of PHP related projects.