This information could be very helpful to those who don't know about it, however it is especially helpful if you run a guild or PUG random folks for raids.
To view a character's history in regards to what Guild's they have been in (and how often they change guilds):
Go to http://www.warcraftrealms.com/charhistory.php
It will request you to enter:
Server, Region and Name are the only ones really needed. However the more information you put in the more exact the search will be. Mind you, this search IS case sensitive, so if you don't capitalize the first letter of the name, it will tell you that is can't find it.
After you enter the search parameters, a page will load where you can click on the Character name that the search found.
Once you click on the link, you will see all the information on what Guilds that character has been in since the character was first found on Armory.
I will caution that this site doesn't update it's information daily; so there can be times when a guild that character has been in isn't listed.
However, it's a good way to find out if that character IS the toon you remember or track the history of a character's loyalty.
I do hope you find this helpful.