Did you know SketchUp models - any SketchUp entity for that matter - can contain Attributes? In SketchUp parlance, an Attribute is a Name/Value pair. You may not have known about it because there is no UI to access them.

This Ruby/HTML/JavaScript project aims to address that omission. Any selectable object can manage their attribute dictionaries (called 'categories' here) and name/value pairs (called 'attributes' here) using this script.

Just unzip the bundle in your Plugins directory and you're good to go.

This plug-in doesn't handle custom UIs for specific attributes or categories, but it could (should?) be extended to do so.