Argent Dawn EU Horde (RP-PvE) has 4 active boxers now:

Me - 5 box mixed group
2nd - 5 box shamans
3rd - 3 box shamans, 3 box palas
4th - 3 box locks, 3 box druids

We don't have a guild, instead we all just use a channel to communicate. "/join mb"
The realm community is awesome here.