Casinos

Casinos are generally considered to be a game created by players using the  mechanic. Casinos are not a mechanic of the World of Warcraft game, and may or may not be considered spamming and scamming.

Terms of use
The following are quotes of the official Terms of Use Agreement that are relevant to casinos.

US Terms of Use
See here for the official most up to date version. (ii) Carry out any action with a disruptive effect, such as intentionally causing the Chat screen to scroll faster than other users are able to read, or setting up macros with large amounts of text that, when used, can have a disruptive effect on the normal flow of Chat;
 * Part 9, Section B

(iii) Disrupt the normal flow of dialogue in Chat or otherwise act in a manner that negatively affects other users including without limitation posting commercial solicitations and/or advertisements for goods and services available outside of the World of Warcraft universe;

(iv) Sending repeated unsolicited or unwelcome messages to a single user or repeatedly posting similar messages in a Chat area, including without limitation continuous advertisements to sell goods or services;

(vii) Participate in any action that, in the sole and absolute opinion of Blizzard, results or may result in an authorized user of the Game being "scammed" or defrauded out of gold, weapons, armor, or any other items that user has earned through authorized game play in the Game;

(iii) Anything that Blizzard considers contrary to the "essence" of the Game.
 * Part 9, Section C

EU Terms of Use
This is from the English version. See here for the official most up to date version.

(2) Carry out any action with a disruptive effect, such as intentionally causing the Chat screen to scroll faster than other users are able to read, or setting up macros with large amounts of text that, when used, can have a disruptive effect on the normal flow of Chat, or using tools that distort or interfere with oral communication of the users;
 * Part 4, Section 2

(3) Disrupt the normal flow of dialogue in Chat or otherwise act in a manner that negatively affects other users including without limitation posting commercial solicitations and/or advertisements for goods and service available outside of the World of Warcraft universe;

(4) Sending repeated unsolicited or unwelcome messages to a single user or repeatedly posting similar messages in a Chat area, including but not limited to continuous advertisements to sell goods or services;

(9) Participate in any action that, in the sole and absolute opinion of Blizzard Entertainment, results or may result in an authorized user of World of Warcraft being "scammed" or defrauded out of gold, weapons, armor, or any other items that user has earned through authorized game play in World of Warcraft.

(5) Anything that Blizzard Entertainment considers contrary to the "essence" of World of Warcraft.
 * Part 4, Section 3

Blue posts
This is a collection of blue posts explaining the official policy on layman's terms.

In game mail
In February of 2008, some players received the following emails about casino gambling:

This mail was confirmed as legitmate by a Blizzard poster on the forums shortly after: