What is your opinion on "Advergames?"

Advergames are games that are usually provided for free, but in their concept and gameplay advertise a product. They are generally commissioned by the company who puts out the product in question, rather than being simple product placement in a traditional game. Some examples of this are the Toyota Yaris game and the Doritos Dash of Destruction game on Xbox Live Arcade. Are you willing to play free games if they're trying to sell you a product? Do you know of any that are actually fun to play (these games usually kind of stink)?