[Requiem]

Multiplayer online role-playing games started back in the days of mainframes, text-based terminals, and Multi-User Dungeons, or MUDs. It was not until the rise of both the personal computer and the Internet that these adventures moved forward into a graphical world. Early experiments such as LucasArts' Habitat, released in 1985 on the Commodore 64, showed some of the difficulties involved in bringing a large number of players into the same online world. Issues such as player-versus-player killing, bug exploits, and the fact that players would blast through new content much faster than the developers could create it, became standard problems that each online game developer would have to solve.
With each new technological advance, the population of online worlds increased. 3DO's Meridian 59 (1996) passed the 50,000 subscriber mark, and Richard Garriott's Ultima Online (1997) reached the 250,000 subscriber threshold in six years. Sony's EverQuest (1999) would double those numbers.
The big surprise, however, was Blizzard's World of Warcraft, released in 2004. It quickly surpassed all its rivals in subscriptions, passing the six million mark in February of this year. Now, according to the web site MMOGCHART.com, it has hit a new milestone by moving past the 50 percent mark for market share of massively multiplayer online games.

Just thought this was interesting.. You can read more about it here:
http://arstechnica.com/news.ars/post/20060601-6964.html