Facebook is going to show their ads in News Feed from January 2012. Currently, ads are displayed in the right column. From January, they’ll occupy the main news feed.

You will only see Sponsored Stories in your news feed about your friends or people you are connected to. You will never a post from a page you are not a fan of, or from people who are not your friends. We want to be really thoughtful about this, so we'll have a lot of rate limits in place. We hope to show people no more than one Sponsored Story in their News Feeds per day and we'll clearly label the story. They'll also be of the same size and treatment as other stories in News Feed.

- Annie Ta, Facebook spokesperson, told ClickZ News
These changes will be implemented gradually from January 2012. The pricing of the ads and other details have still not been disclosed.