i think it will be better, if users can install new theme/applet/extension from cinnamon-settings (not from website download).
It will be more comfortable and easier to newbies.
I imagine that it could be something like applet installation in Gnome 2x(Ubuntu 10.04 - right click at panel, add applet and broswe gallery).
It could be based on applet lists updated with apt-get update and installed through apt-get install > comfortable for everybody.
Sorry for my bad English.
I would like to see something similar to this for cinnamon.
At least it would give the cinnamon firefox plugin a purpose.
Closing - this is in the works.