Before I started to read this paper on MMO gambling, I balked a little at the article title "Internet Gambling and the MMORPG." I remember the joke-y bingo game some clever WoW players created, but thought little of it. Mark Methenitis, however, didn't. He authored the aforementioned paper and in addition to gambling, Melethenis takes a long look at the rise of virtual economies and their penetration into very real world wallets. It's a looooooong read, but one of the best I've come across.

Internet Gambling and the MMORPG [Mark Methenitis' Texas Tech Law Paper]