Even the most useful plugin suffers from adoption if it's difficult to install. And asking users to simply walk through an installation wizard to conduct the installation may prove to be too much. Widgets certainly offer an ease of deployment solution.
Here's an excerpt from the download page within IBM:
All widgets may be installed in Lotus Notes by dragging the widget's image to the My Widgets Side Shelf view in Lotus Notes. Expeditor users may install via the update site.The image is simply an IMG tag which references an XML file. By dragging the image to the My Widgets side shelf view, Notes and Expeditor will process the XML and install the Eclipse plugin with ease. Many of my widgets sit in the side shelf as well for convenience. But to be clear, widgets are not UI elements or Java types, they are a framework for delivering you plugin - an easier way to install an update site. So any Eclipse plugin that contributes to the Platform can be delivered as a widget - it does not have to be a side shelf component or Notes UI add-on.
To install, simply drag the widget images on this page or links on the project's file page into the My Widgets view. If the My Widgets view is missing in your Notes client, access File - Preferences - Widgets. Make sure the "Show Widget Toolbar and the My Widgets Sidebar panel" checkbox is selected.
For reference, here's how the widget's XML might appear:
<?xml version="1.0" encoding="UTF-8"?>
For more information check out http://www.ibm.com/developerworks/lotus/library/notes8-widgets/