In a new post to his blog Ulf Wendel has pointed out that the mysqlnd query cache plugin quickstart is posted on the docs.php.net site.

New in the PHP manual: a quickstart for the mysqlnd query cache plugin. PECL/mysqlnd_qc, the mysqlnd query cache plugin, is transparent and ease to use. But, how? Some pointers have been given in assorted presentations, here on my blog and in some, few examples from the manual. Fixed. You can now browse a quickstart to gain a quick overview.

The query cache plugin can replace the query caching MySQL does and can help with things like multiple storage options (memory, APC, Memcache, etc) and almost no changes to your application. There's also a method (mysqlnd_qc_get_query_trace_log) that comes with the plugin that gives you a "stack trace" of every query run through the MySQL interface.