Hi!
 
with a linear listing we can then take this widget and put it _right inside_
the PanelController widget. so when the user clicks "Add Widget" in the panel
they get the PanelController but with your interface in it. 

Neat! :)

for the desktop, we can just throw up a very simple panel style widget at the
bottom of the screen .. if there's a panel down there, it would even pop up
the panel controller for that panel in add widgets mode. if there is no panel
down there, just throw up this custom widget.

Got that! That's nice
 
this is trivial work and, again,
something i or someone like me can put in place for you so you can continue to
concentrate on the Add Widgets interface instead of learning how the plasma-
desktop shell is put together ;)

Ok, if you're saying so, fine by me! :)

the category picker will be the tricky bit, i think. but we can
discuss this more later (i think i'm already probably flooding you with input
here.. sorry :)

The idea of Marco is nice and is probably one of the few ways of arranging this list: "having a list of toggle buttons that permits to check an arbitrary number of categories?" Maybe laying next do the search box, above the applets list?!

Well, I would just need a visual confirmation that what is on my mind is the same of what is on your mind and on Ivan's and everybody else's mind. Sometimes the words just can't describe everything that's our mind, right?! :)
Mocks of these new ideas for the new PAB have to be done so that the work comes out exactly like everyone expects! So, can anyone provide me some sketches or mockups ?! Please?! :)