Just a note on Urban Spam, I think you're right that in these creative brainstorms we always ask two major questions: is it on brief & is it going to break through. But I think to be fair to us & our process, we also always ask: is it going to be relevant & engaging? I think those are two very key questions when it comes to ambient media & whether or not it's seen as SPAM or Insightful.
It's true the reality is that people get turned off by too much "in your face" advertising. But I'd argue that if something is really engaging/entertaining (a la Altoids Tugboat), than we're half way to a great idea. When it comes to ambient advertising, we definitely need to learn as an industry to filter ourselves (just because it hasn't been done before, doesn't mean it should be done), but I think we can do some great creative that works for the brand & the consumer.