There is a game set to take the Xbox360 by storm in the next few months called "Mass Effect." The game is developed by BioWare, which also created the "Star Wars: Knights of the Old Republic" series. The company's games have generally focused on gameplay with a very complex and detailed "choose your own adventure" type of structure. Players make decisions in forging friendships or rivalries, and these decisions can have a massive effect (hence the name of the new game) on the game world.
What this kind of feature offers to branded games is huge. Imagine a standard survey incorporated into a game scenario, where the content and participation in the survey is the payoff for the users. This could be something like Ford creating a game where users create their own cars, putting a limited number of points into features like safety, gas mileage, performance, and design -- getting information on what that user is most interested in, and the user then getting a game experience customized to him. That customization is the key element. Someone putting major points into safety is not going to be happy to play a racing game, where performance would be the desired metric. This would also skew the results of the "survey."
Putting backchannels for information into branded games could be very successful, but the experience must be complex and have equal payoff for each "answer." Marketers using games as a tool might want to get a feel for the system done well from the BioWare games, and then consider implementing a similar system with a backchannel for information in their own offerings. They might be pleased with the "effect."
Simple marketing intrusions (nokia phones in Splinter Cell, the sidekick being your device of choice in the Def Jam franchise, etc) all caused cringe inducing reactions to gamers.
A marketing survey, and the questions they ask, are far different from the Bioware model, which is more about exploring "personality" and "morality." The dialogue trees in their games and their cousins (everything from the original Baldur's Gate to Neverwinter Nights 2) are more about exploring options for interaction and solving problems, rather than aquiring information from users.
I have little faith in marketers that aren't hard core gamers, or developers that aren't marketers implementing such "backdoor" features. A safer (smarter) solution would be giving the users a choice of taking the survey for some in-game item. MMOs are perfectly suited for this: fill out a survey, provide your account name, get an in-game item.
When advertisers start making games the results are very rarely pretty.
Customization is a key element, though I must say: If I was dealing with the fate of the universe and took a break to interact with a terminal in game (e.g. Deus Ex, Doom 3) - thinking I was getting more back story or character development and I was swindled into offering my opinion on mouth wash, I would be "helleva" angry... Even if it was for a special edition jumpsuit for my avatar.