With the coming of Cataclysm, class mechanics changed, preferences changed -- and in many cases, main characters changed, leaving guildmates wondering, "What do I call him now?" Thankfully, some forward-thinking types already have naming schemes in place to ease the transition. Several members of my guild use the same three-letter prefix for every character name to eliminate confusion, while others use a full word preceded or followed by a class-specific descriptive term. We have an officer who uses some combination of the same few letters, making his characters easy to identify, and one tank even uses a food-related theme.
Of course, even this does not completely eliminate the confusion, except in cases where the same prefix is used. We still have folks being called by the names of characters they have not played in a year or more. For those without the forethought to create a theme, members are often left checking guild notes to discover who they are talking to. As one of those forethought-lacking players myself, I often wish I could go back in time and find a way to connect my character names and make things a little more obvious.
Do you know someone with a great naming scheme, or do you have one yourself? How did you choose? If you don't have a gimmick, how do you handling telling friends and guildies what to call you when decide to make a change?