Argent Dawn EU Horde (RP-PvE) has 6 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
5th - 5 box druids
6th - 4 box shamans / 4box paladins

We just started the merging together in multiboxing guild Lok Narash, and for those still outside we use channel to communicate. "/join mb"
The realm community is awesome ad mature here.