Of course, every time a company engages in a publicity stunt like this, the same debate we're all having takes place.
Pro: "Wow, what a great campaign!"
Con: "Pshaw, it's just a gimmick."
Pro: "Oh really? It got you talking about it, didn't it? So clearly it must be working."
Con: "Grrrrrr..."
The only reason why we're having this discussion here, on Hacker News, is they happened to choose flavor of the month Twitter as the focus of the stunt. Wow, so they have the ability to discern what the hottest meme on the web right now is.
They could have also given Brad Pitt and Angelina Jolie a million dollars to shave the Skittles logo on the back of their children's heads. If they had done so, no one would here would give a shit, but I can guarantee you the message boards at Perez Hilton and celebritybabies.com would be lighting up with the exact same conversation we're having here.
You will convince me that this is something more than a gimmick if one month from now ANYBODY is still taking about this or visiting that page. Actually, if they're even still USING the Twitter stream as their home page a month now I will be halfway convinced.