This. As much as it may work right now, because basically no one is doing it, as soon as it becomes a popular method, it seem to me it will stop working pretty quickly. Everyone doing it will become equivalent to a Jehova's Witness knocking on your door.
That said, I imagine I'd be more okay with it if every time I said yes I got a free coffee.
Aside: I wonder how different reactions would be in different countries/cultures.
In Mexico people try to trick you by asking something for something innocuous, like the time, and then ask you for money.
Also a supposedly common scam is to get personal info such as names and phone numbers in surveys and, later, to use this information to make fake kidnapping calls sound more plausible.
The upshot is that you learn to ignore people who try to get your attention. I don't think it would work too well here.
On that note, I'd imagine that "don't ask for ANY personal information except an email address, right at the end" is a pretty good rule for this sort of testing anywhere in the world. Good point!
The technique is somewhat self-limiting. Unlike, say, email spam or online annoyances, you've actually got to be there in person for it (though sufficiently large organizations could hire bodies for the purpose).
Still: the method has significant costs. That's a good think in the "preventing overuse" department.
To me, what made what he was doing appealing was that he wasn't directly soliciting people. He made the arrow and the sign. He wasn't harassing anyone in line. I think that makes all the difference.
That said, I imagine I'd be more okay with it if every time I said yes I got a free coffee.
Aside: I wonder how different reactions would be in different countries/cultures.