People are becoming really good at ignoring advertising, so advertisers are forced to become more creative about placement and context. As a designer with who loves creative advertising I applaud this stuff. But I'm torn. Of course it's more intrusive than a billboard you can ignore. But does the cleverness make it more acceptible? Is it actually less intrusive because they don't have to be huge billboards (that obstruct natural views or cityscapes).
Take a look at about a dozen creative ad placements from around the world. What do you think?

In this example, a life-size Mini at the top of a subway entrance/exit in Zurich gives passersby the impression that an endless stream of people are emerging from (or entering) the car. It's creative genius, but does it go too far? I mean, as a citizen I think it would make me smile because it's so clever. But honestly, if the street becomes full of this kind of gimick I think I would begin to dislike advertising more than I already do.
(Thanks Sarah for the link.)