It is against Blizzard Terms of Service to use or Endorse private servers. As per the Terms of service:
"4. Responsibilities of End User.
B. You agree that you shall not, under any circumstances,
(iv) facilitate, create or maintain any unauthorized connection to the Game or the Service, including without limitation any connection to any unauthorized server that emulates, or attempts to emulate, the Service. All connections to the Game and/or the Service, whether created by the Game Client or by other tools and utilities, may only be made through methods and means expressly approved by Blizzard. Under no circumstances may you connect, or create tools that allow you or others to connect, to the Game's proprietary interface other than those expressly provided by Blizzard for public use.""
While Warcraftfanon and Wikia are not directly associated with Blizzard Entertianment, we will not encourage the use of private servers.
Content related to Private Servers (Characters, guilds, locations, storylines etc) may be posted on Warcraftfanon. However, no endorsement of Private Servers will be allowed. Private servers will not be named in the course of articles. Links to Private Servers as well as contact information will also not be provided either in articles or user or talk pages. Images generated on Private servers (eg, Screenshots) will also count as endorsement and will not be permitted.
The policy will be applied retroactively from September 1 2008; existing articles will be edited to remove such references. Failure to comply with this policy will result in editing and/or deletion of content in violation of policy.