I had a very fun night the other day hanging out with guys from the GRL Australia - Perth. They mentioned that they have been trying to get the drawing pad wireless without doing anything too fancy and I thought about VLC screen streaming. It can get pretty nice and recursive if done incorrectly as shown below. If VLC runs off-screen and the graffiti drawing app runs in full-screen then we can easily send off the drawn work to the projector connected to say small computer (Gumstix strikes again) running VLC in full screen mode.
So we have Graffiti App->Screen->VLC->Over Air->VLC->Second Screen/Projector. I would have drawn a nice block diagram but the GRL folk can do that.
Now here is the second interesting part , some projects such as LightTwist and PixelFlex do camera based projector auto-calibration. Why not use the same ideas and build multi-projector graffitis, also we have a camera image to display to the tablet user as the surface on which the graffiti is going and the auto-calibration can ensure what is drawn goes where it's drawn including messy mesh manipulation etc. giving the feel of real graffiti drawing. So here is another flow:
Camera->VLC->On Air->Drawing Pad->Back ground to Graffiti drawing app.
For now it can be just a static image, eventually proper feedback will help with colour selection and positioning elements of the drawing.