The oik debug filters plugin for WordPress helps you to track down PHP notices. The plugin is no longer required; it’s been integrated into the oik-bwtrace plugin.
Have you ever seen a notice like this this and wondered where it came from?

Notice: has_cap was called with an argument that is deprecated since version 2.0!Use the oik debug filters plugin, in association with oik-bwtrace to find and fix the bug!