Does MW3 support cross-platform multiplayer?

Does MW3 allow PC, PS3 and Xbox 360 users to play together?

How does the matchmaking work? Is it more like in Valve games, where users just select their servers, or more like console matchmaking, where you join as a group and wait to get matched?

It does not - the three platforms (PC, Xbox360, and PS3) are all distinct, separated multiplayer platforms (PC servers, Xbox live, and PSN).

This would require PSN and Xbox Live to interact via an agreement between Microsoft and Sony, which is unlikely given that they compete. Additionally, the PC version supports dedicated servers and official servers, with VAC protecting against possible cheating.

This has been a feature people have wanted since multi-platform releases started to hit the shelves, but to the best of my knowledge has never been implemented (please correct me if you can think of a good example, I'm sure at least a handful of games have made the attempt).

Aside from the technical challenges, there are balance problems with cross platform play between the PC and consoles. Having a mouse gives the PC player a serious edge, they can aim quicker and with greater accuracy. This is why many console games have some sort of "aim assist", which is a rare and generally unnecessary feature on a PC.

To give a more extreme example, imagine playing a game like Starcraft from a console against a player on a PC. You would be screwed, the pc player has a huge assortment of shortcuts and hotkeys in front of him, while you would spend your time slowly panning around the map just to keep units building.

While there are things that could be done to add balance, such as the previously mentioned "aim-assist", such features would cause social problems. The console players would feel cheated when a PC player headshots them with a mouse, and the PC players would feel cheated when a console player headshots them with auto-aim. Dying because you were out classed isn't fun, dying because the other player had some perceived advantage is even less fun. This is why people get upset with campers, and also why so many games have adopted a kill-cam.

Even without the psychological aspects, two people might be good at the same game for different reasons. Take for example to console players, one who gets kills through tactics, and one who gets kills from having excellent aim. Any artificial balancing against PC players would affect the two console players differently. While it's true that life isn't fair, games are more fun when they feel fair.

In my opinion, this is a technical problem that is best resolved with a business solution. I could imagine some sort of scheme where for less the full cost of buying the game twice, I could get a "multi-platform" version. Kind of like what we see now with blu-ray DVD combo packs. There would have to be some mechanism to prevent the resale of the second copy to keep the publishers happy. A shared two step authentication method is one possibility, although I'm sure there are better solutions out there.

So far, the only game I know of which two different platforms run on the same server is Final Fantasy 11. At the time I played it, it was both PC and PlayStation 2.

I have Call of Duty®: Modern Warfare® 3 for the Wii, and as it was said before, there would be some serious advantages as far as controls go. I wouldn't want to get owned by some kid who has easier controls.