This is a great marketing campaign. $1.3 million a month isn't a lot of money for a company like Pepsi, but they get a lot in return. The brand engagement will be huge, it is likely to go viral on some level. It gives their brand a good name. It gives them an excuse to advertise their brand at the execution of the ideas too, without looking like an evil corporation exploiting a good cause.
Hmm...Since it's not valid for people outside US so I wont be able to participate but would I have participated had it been valid in India?
Let me think...Probably Not. I have lost any hope that such marketing campaigns can ever solve real world problems or help in nurturing the next big idea because that's not the main motive behind such campaigns.
The motive is to engage as many people as you can and that is bound to happen after having a look at the site, which is rather attractive and from a designer's point of view quite appealing.
Pretty smart, if you ask me.