I've been fighting the Component Model to the ground and found this interesting tidbit: Forms cannot be added to the toolbox by default. Your custom forms need to set some attributes to make it work.
The Designer/Component Model is quite the body of knowledge to wrap one's head around. I have Chris Sell's book and Mathew MacDonald's book on order. Are there any other good books on integrating with the Designer?
By the way, here's my problem:
I've subclassed the Infragistics UltraToolbarsManager and placed my subclass on the toolbox. Now when the UltraToolbarsManager Toolbox Item is dragged on the canvass, several assembly references get added. When I add my own control, I just get the assembly of the control. How can you tell the designer to add the appropriate assembly references?