Counter-Strike Gets In-Game Advertisements describes the addition of ads to Counter-Strike and Valve Did Not Approve In-Game Counter-Strike Ads is a follow-up revealing that this has been done without Valve's permission. There's more on this on Shacknews where they have learned this all seems to be arranged between server operators and an agency for the advertisers (thanks Frans). Also, a new Steam Update has a screenshot of the upcoming remake of the Militia map for Counter-Strike: Source.