Once drawing happens on the scale of a wall it becomes social. It occurs in the realm of physical interaction. Conversation, language, human drama are natural components of the experience.
I found the game aspects of Scrawl to be exceedingly fun. Being interrupted by other art is one of the luxuries of being an artist. Usually the interruption comes in the form of imaginary conversations with dead guys. How fantastic to have live-artists interrupt you mid-drawing. How fantastic to incorporate interruption into your work by agreeing that the borders of your piece are completely up for grabs.
"ArtSPACE presents SCRAWL!: Drawing Writ Large"