Have you every had a time when you have added two of the same widget to a sidebar and wanted to style them differently? You may have run into problems as they have the same CSS classes etc. and the ID they are given is random. This is why I created the Simple Widget Classes WordPress plugin.
The plugin simply adds an additional text input box to each widget added to a sidebar in the admin. In here you can type the names of any classes (space separated) that you would like to give to the widget. This can then be used for custom styling.