In the future to prevent overload from occurring, take a page from Guild Wars books and do a "Guest" Server pass that temp allows you for 12 hours to transfer your character and all its stats/gear/etc to another server. Allow 2 passes per 24 hours, that are free and ready to use at the character selection screen. Make the Market system Cross server as not to conflict with this system. Allow players on NA servers to cross over to other NA servers, JP to JP and EU to EU.

This would alleviate some server strain in the future and give people a chance to play with friends across other servers.

It would also promote a stronger community, when people need help with something they can post it and jump to a server where others are offering help or need help as well temporarily without upsetting the flow of the game.

To make a permanent transfer you can still charge people, many will want to do a perm transfer because they will want to be with friends or family.