One essential ingredient of MMO gameplay is the synchronization of various events and special effects across multiple systems. A boss fight would get hairy pretty quick if everyone in the battle wasn't experiencing the same environment simultaneously. A New York-based company has sued several MMO-makers, claiming the games make use of a patented data sharing technology.
Paltalk Holdings, Inc. has filed suit in Marshall, Texas against Activision Blizzard (World of Warcraft), Sony (EverQuest), NCSoft (Guild Wars), Jagex (RuneScape), and Turbine (Lord of the Rings Online). Paltalk specifically chose the east Texas court for its history of favoring plaintiffs in related cases. The patents in question basically cover sharing data between connected computers so that users are presented with an identical digital environment.
Paltalk took Microsoft to court in 2006 over the multiplayer technology used in its Halo titles, and successfully strong-armed Redmond into settling out of court. I imagine that will only strengthen their present case, as it adds some level of validity to their claims.