Google's main revenue stream is generated from online advertising, however most recently it started venturing into television, printed media and radio advertising. Back in March 2007 Google acquired AdScape, a small company focusing on video game advertising. A patent filed in 2005 by Google to lock in a method for in-game advertising recently became public several weeks ago and has been attracting some attention since then.
I can imagine not only the gaming community won't be happy to see their games flooded with advertising, but given the nature of this method which aims to monitor gamers' behavior, it probably won't be popular among privacy advocates either. The patent summary reads:
"Information about a person's interests and gaming behavior may be determined by monitoring their online gaming activities (and perhaps making inferences from such activities). Such information may be used to improve ad targeting. For example, such information may used to target ads to be rendered in a video game being played by the person."
In-game advertising is nothing new, and given recent moves by Microsoft and Intel on the market it makes sense that Google wants a piece of the pie too. With the production cost of games soaring, in-game advertising provides a way to earn some extra revenue many game developers will take.