A few years back I had a drawing notebook I started doodling in. A friend of mine doodled in it and passed it back to me, so I doodled some more and passed it back to him, and so on and so on - thus the group sketchbook was born. I started bringing the book with me to gatherings and jams and parties, and people would pass the book around adding their bits. Afterwards I would bring the book home and integrate all the elements of the previous event's drawing into a theme of sorts. I keep meaning to pick up another blank drawing book...