Blizzard is now offering a suite of new guild services for guilds looking to switch servers, factions, guild names, and more.
Transfers and faction switches will carry over important guild data such as name (if available), guild leader, guild bank, etc. If a guild member decides to go along with the move, they'll have to pay their own way when transferring servers or switching sides, but they'll be immediately part of the guild once the transfer is complete. Easy!
There is one caveat though, the launch of the new guild services is currently limited to a select number of servers.
You can find the full list of servers and a new Guild Services FAQ over at the official World of Warcraft blog.