Today Google announced that you can demographically target ads showing up on its contextual network as part of a new beta test. But back in 2006, Google rolled out what seems to be exactly the same feature.
In 2006, Andrew Goodman noted that targeting was added. It allowed for these types of things:
Annual Household Income (USD)
They also offer advanced options for demographics, which includes:
Related Topics: Channel: SEM | Google: AdWords