Infinity Ward have posted a heap of information regarding the PC version of Modern Warfare 3 over here. Highlights include some details on how the dedicated servers will work - "Dedicated Servers, allowing players to find and filter via an in-game server browser or set-up their own Dedicated Server for complete control, without being restricted by any 3rd party hosting requirements. If looking for a Dedicated Server to join, if you choose not to set up your own, you can filter and favorite by Ping, Map, Gametype, Hardcore Variants, Voice, Password, and many other options" (such as RCON) - and also graphics: "including enablingand disabling of new rendering features such as SSAO, you'll also be able to modify DOF, Shadows, Anti-Aliasing, Texture Resolution and more." It will have Steamworks integration, with VAC as the anti-cheat system, and will also support LAN play.
That is a lot of stuff!