Four trailers have been released showing four of the locations: Germany, France, America and England.
And going by leaked info and screenshots, this game is supposed to be set in World War 3. Robert Bowling has said that some of the leaked info is accurate, and other bits is inaccurate.
Anyway, according to Kotaku, the source for all of this mess, MW3 is to have large scale maps and destruction, though that is most likely for campaign only.
Things are looking good.
If you havent seen any of the screens, here ya go: http://kotaku.com/5801353/modern-warfare-3-multiplayer-features-battles-in-brooklyn-clash-in-mogadishu/gallery