Valve issued a press release today confirming that Call of Duty: Modern Warfare 3 on PC will make use of Steamworks and will feature Steam achievements. The game is available for pre-purchase (€59.99) on Steam as of today.
"The PC version of the product will be powered with Steamworks for both the digital and tangible versions of the game and, as with all Steamworks titles, offline play will also be supported along with Auto-Updating, Achievements, and more. Call of Duty: Modern Warfare 3 will also support dedicated servers on day 1."
It still looks as if Battlefield 3 will opt out of a Steam release, because of the feud between EA and Steam over in-game DLC purchases.