This concept needs to be applied to GNOME's Panel when adding new applets. The current method of adding applets just lists a bunch of applications with only alphabetical organization. Chances are very good that you only want to have a few of these. Maybe some you'd like to hide (Brightness Applet? Kind of useless on my desktop.), maybe some you'd just like to be able to find quicker.
My proposal is to add categories and use an interface similar to that of CCSM. I have created a mockup in Glade to reflect this:

I did the mockup in Glade rather than the GIMP for several reasons:
- It shows how simply it can be done in GTK+; each menu button is a GtkLinkButton
- It gives authenticity in the outcome: this is how the dialog will look (see notes below)
- I can easily change the mockup based on GTK+'s rules, adding any suggestions I may get
In the current version of GNOME Panel, you have a set of buttons on the bottom of the dialog (i.e. "back" and "add" or "forward"). Whether the button reads "add" or "forward" depends on what you are adding. If each applet is clickable to bring you to the next stage, you no longer need to press this button.
In my concept, when you click on an applet on the right, the content of the dialog will change to reflect that applet. The menu stays on the left, displaying information about the applet and offering a "back" button in case of a misclick.
Notes:
- The icons are merely placeholders, as are the items themselves. Categorization of applets can wait for another day.
- CCSM has a different colored background for the icons on the right. It would be beneficial to have that in this dialog as well.
Comments or suggestions? I'd love to hear what you think, good or bad. You can also leave comments on the Bugzilla entry.