The note from Joi Ito’s web about the arrest of the organizer of something called Bikes Against Bush is interesting (aside from the fact that you can get arrested for being in NY with a bicycle nowadays.)
The technology of the dot-matrix printerbike is very cool, but isn’t it a little too complicated? I remember reading from one of Hemingway’s books about people walking around the streets of Paris with a rolling drum which would paint the word “Cinzano” on the sidewalk in water – which would, eventually, evaporate, hence no need to clean up at all.
This bike, ingenuity aside, strikes me as a high-tech answer to a low-tech problem. Still cool, though.
Applied Abstractions 
I see this as a pretty shrewd use of memetics: the bike thingy has turned out to be an effective carrier of the secondary (anti-Bush) message, with coverage in all manner of media (even “Popular Mechanics”) as well as the blogosphere, precisely _because_ it looks like something out of Rube Goldberg (or Kjell Aukrust, for that matter).
The “Cinzano” story you mention can be interpreted the same way. By printing with water the physical message will last for a very short time, but the printing method is sure to capture the imagination of many. As it did with Hemingway, leading him to do a bit of product placement for free. 🙂
Ingenuity is the weapon of choice for many things….