Duplication. Though the Mew Glitch was very useful, duplicating any item or pokemon is even more useful.
Back into lawsuits...
Yuri Gera, the psychic who sued Nintendo claiming that Kadabra (whose Japanese name is Yungera) was an unauthorized version of himself, and furthermore that the star on Kadabra's forehead and lightning bolts on its belly were anti-Semitic, making Yuri Gera look bad
or
the two parents who set up a website called Pokemon Kills after their son choked to death on one of Burger King's plastic pokeballs (causing Burger King to immediately stop selling the pokeballs and recalling them for various other Burger King food items)