Sounds like a great idea, and would be a great addition, as well as a compliment, not replacement, to the already provided guild tab.
On the server you are on, alot of your "buddies" can be in your guild, and it would be so much easier, especially for leaders at least like me, to be able to distinguish who in your buddies is also in your guild and on tag. Then if you need to see other servers, you should be able to go to the guild tab, and see ALL GUILDS.
Would be helpful.
