Ambient media, or urban spam?

I was in a brainstorming a couple of years ago for Five Alive, the Coca-Cola juice drink brand.  The tagline is "Feel Alive" and so someone from the media agency suggested the idea of hiring people to ride around on buses and subways and randomly get up and shout out "I feel alive!," do a little dance, then hand out cans of Five Alive.  Fortunately, that idea didn't go anywhere.  But I started thinking about it again this week, what with the announcement of advertising starting to appear on air-sickness bags and eggs.  What makes an ambient media idea good or bad?
 
It's relevant because a bit of a schism seems to be opening up in the industry on the use of guerilla/ambient media.  On the one hand, it's become pretty standard to generate some ambient stuff on most projects, to "see how big the idea is."  And those ideas that get produced seem to be winning their share of outdoor and media awards.  JWT now does a monthly video roundup of ambient and other 'brand stunts' from around the world (they're all on YouTube: watch the most recent one here).

But there's also been a bit of a backlash brewing against the rampant plastering of ambient on every surface we can find.  While consumer-culture commentators like Adbusters and StayFree have been critical of marketing encroaching on public space for a while, what's interesting is the backlash is now coming from within the advertising industry itself.  The phrase "urban spam" was coined by designer Rob Forbes, and then planner/blogger Russell Davies started commenting on it (Russell went as far as creating printable "Stop Bothering Me" cards you could hand out to sampling teams and other street marketing types).  Now trendwatching firm PSFK has put together their own video against urban spam, in an attempt to start some dialogue in the industry.  And it seems to be working - people are starting to talk. The funny thing is PSFK's video looks remarkably similar to JWT's videos.  One man's trash is another man's treasure.

Personally, I think ambient stuff when done well can be wonderful - like all the great Mini stuff from Crispin Porter and Taxi a few years ago.  But I have to agree with PSFK.  There's getting to be too much of it.  We evaluate ambient ideas by asking "is it on brief?" and "will it cut through the clutter?" - but we don't ask ourselves "is it going to be annoying?" or "will anyone care?"  Just because we can't interrupt people on TV as much anymore doesn't mean we should be looking for lots of other places to interrupt them.  Is that really the best we can do? 

So is ambient a creative way of surprising hard-to-reach people who are increasingly avoiding broadcast advertising?  Or the last gasp of an interruptive advertising model that provides decreasing returns and should be allowed to die already?  Or is it all in the eye of the beholder?   Any thoughts?