Microsoft has just received a patent for an interesting feature in squad based co-op shooters.  US Patent #7559834 was filed back in 2002, but only just got approved by the United States Patent Office.  From the description, timing and pictures - it appears to be for the 4 player co-op game Brute Force from the original Xbox.  

A squad-based shooter video game allows players to dynamically join and leave the game, while that game is in progress, without the players having to save and restart the game. When a new player joins an in-progress game, a new squad member is allocated to the new player and the screen is split to present a viewing panel for the new player that depicts scenes from the perspective of the new squad member. When an existing player leaves the game, the screen is unsplit to remove the viewing panel for the exiting player and that player's squad member becomes part of the squad being controlled by the remaining player(s)

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