OSXBytes

How to use iTrash:
Drop any application, widget, prefpane, plugin on the main window. iTrash will now search for related files (.plist files, data, caches, ...) and shows the results into a list.
When you are sure you want to delete those files you can press the delete button located at the right bottom.

Expert Mode:
In default mode iTrash already find most related files. However, sometimes developers of applications uses not so obvious data file names and most uninstall tools do not find those files.
iTrash uses a Levenshtein Distance search algorithm which can trace down more possible related files.
You can switch to Expert Mode in realtime by turning the switch to ON. iTrash will search again but more thoroughly.
Sometimes it will find more related files but it is recommended to verify if the files are indeed related.

Ghost Mode:
You can enable Ghost Mode in the preferences. When enabled iTrash only pops-up when you drop something in the trash.
Every time you boot your system Ghost Mode will run in the background. This mode does not use any CPU load and is safe to use.

Applications List:
This feature is handy when you do not know where the application is installed. Double clicking the basket, pressing cmd+L or choosing Menu "Applications List" a new window will be shown with all installed applications, widgets, prefpanes, ... on ALL volumes. You can also hide all default OS X applications, widgets, ... from the list by pressing the button on the left bottom.
Check the applications you want to delete and press search.

Lost Files:
This enables you to find related files that are obsolete (Application is not pressent anymore). Because it is very difficult to ensure every listed item is 100% obsolete, it is recommended to check all files. In general it will give you a indication which files can be deleted.