Any like minded group will naturally want to form codified relationships. On the server Proudmoore US there are a large number of Gay/Lesbian/Bisexual/Transgender (GLBT) guilds clustered together. They represent the full gamut of gameplay in WoW, from casual PvP to hard core raiding.
Our own Lisa Poisso sat down a couple months ago with Venfelder of the guild Taint to talk about experiences and life in a GLBT guild. It's quite an interesting read for those wanting to know more about this aspect of WoW's culture.