I play on Xbox's server (Gorefiend) I don't believe he has finished getting epic mounts for all his toons yet but I could be wrong. His guild Clusterfunk actually semi-broke up just recently and joined a larger raiding guild. There is a video of him in arenas I believe its on warcraft movies it has a link to a webpage with lots of videos of his toons in action and several different arena games. Last I talked to him he was running 4 of his shaman and a Paladin friend of his in 5v5s.
When you take into account that a normal person makes a couple of thousand gold leveling from quests etc. Then think of each of the "box's" as a normal player that levels and does all the quests (i would assume they don't just grind), not to mention they could probably 5man instances rather easily its not that hard to believe they make enough to get epic mounts.
To be fair Sam's thread is really only bested by Kate's Thread (VNSFW!) in messageboard lore. Only The Pretty Girl Thread (Oh god, NSFW) has, on any messageboard I've ever spent time on, been a consistant better source of entertainment.
Ironically, I think the Mage thread here has them all beat in the long term.
(EDIT: While being far more educational, although not nearly as interesting in other ways.)
(EDIT: For the non-feint of heart, I recommend the threads above. I've half joked with acedemics I know that a course on the history of the Internet messageboard could be taught based on Kate alone. No, not that the thread is a good thing, only that it is the entire mess that is irc, messageboards, bbc and so on reduced to even less than usual. With a critical eye there is great source for amusement there. Without, there is nothing but vulgarity of course. I find human nature to be endlessly amusing though.)
I think you would have very good luck in arenas. There is a 4 mage/1 warrior arena team that I played once last patch, they destroyed us. Mages all invis at the start and just assist the warrior, whatever he targets dies. I believe 2 were full frost with elemental, and 2 were AP/frost. Healers simply cannot react in time to that much damage going towards one target. Also any melee is essentially permanently frost nova'd.
As someone who dual boxes with a warrior/priest every day I can only imagine how much more intense 5 boxing is. Nice site by the way, I'll be reading through it to see if there is any tips I can use.