When is it ambush marketing?

Windhoek's agency Brandhouse distanced itself from the ad, calling it "ambush marketing". Fair enough. Public response, however, said it was "so clever, Brandhouse should employ whoever was responsible for it".

Again, Marketingweb is aware of the damage that ambush marketing can do to a brand. But if it's as clever as the "We don't smoke before the anthem" spoof was, is it damaging? And, if it's not damaging, is it really ambush marketing?

Brand managers have to draw the line somewhere, but when something goes "viral" in a good way - that is, gets positive mileage with your target audience and is an almost perfect replica of your advertising - should people be speaking of lawsuits?

Nandos is always quick to catch on to "buzz on the street" and demonstrated the talent once again during "Joostgate". Shortly thereafter, someone - we believe it wasn't Nandos or its agency - brought out a spoof ad suggesting certain actions Amor should take in the wake of Joost's shenanigans. As far as we can tell, there was no threat of lawsuits in that case. Why? Was that not also "ambush marketing"?

Another thing, then: If someone comes up with brilliance that may be considered "ambush marketing" merely because he or she doesn't work for the agency responsible for the brand, would that agency consider paying the "ambusher" for the idea?

It's an interesting debate - and we'd like your opinions.