There's several different reasons that I find this offensive. For the camera thing, at the very least, they're wasting your time. Here you are, thinking that you're being a nice person and helping out a couple of people, and it turns out that they're lying through their teeth to try to sell you something. It like emails that use 'friendly' titles to try to trick you into reading it: you wind up with an inbox full of 'How was your vacation?' and 'Haven't talked you you in a while' and you have to check every
one of them because they MAY be legitimate.
Can you imagine the world if this takes off? Every single person you talk to, you're never going to know if they're a nice person or a corporate shill trying to sell you something.
Then you have the 'lets create a buzz on the internet' thing. Suddenly, all the sites that have product reviews (IMDB, amazon, resellerratings, etc) that preciously were useful tools for finding good products become absolutely worthless because they're filled with marketting department spam.
All the boards that exist to discuss movies, games, music, etc - destroyed, overrun by corporate drones spouting advertising slogans. It won't even be possible to filter them out because they're disguising themselves as normal posters. If I post on the "movies & TV" right here on these forums that I really liked a movie, is it because that's my honest opinion, or because Sony paid me $10 to say that? You're never going to know.