I hate to say this but if the game becomes successful whit I would imagine a free mmorpg will there will be allot of people coming from other games. They will use the terms and language they are accustomed to.
The only way to thwart the use of these slang words is for the entire base community to let people using these terms know that they ar not accepted within the context of the game.
I would also like to see a filtering system that could take words like n00b and change them into words such as foreigner, much like they do with everquest on this forum.
Another useful thing would be to convert real life profanities into more amusing or game/character appropriate curses. It could even do this randomly.
Changing a well known explicative like the f-word into something funny or even replace it with another word from the dictionary randomly would cause people to choose their words more carefully.
This topic looks like it is going to fruit some good ideas.
http://www.planeshift3d.com/wbboard/thread.php?threadid=11816&boardid=13&styleid=3