Didn't see it mentioned here, but according to the Prima guide, if a gnome is left in a room with an unfinished sculpture or invention, the gnome may work on it overnight, and the next day , you check it and it is 99% done. The one gnome I have found in my game so far sat next to my front door, until I planted a garden. The next day it was sitting next to the plants, and has been there ever since. I wonder...if it might weed or water for me?
Edit: Nope, just checked the game, and he's dancing with the trash can now *sigh*