The mobs do hit rather hard it seems. Multi-boxing will be at a bit of a disadvantage until the first epic set goes to no rating requirement (or those that get it early on). This is because of the amount of stamina difference between a premade paladin (22k hp) vs a premade shaman (16k hp). The mobs in heroic Halls of Lightning were hitting me for ~3k a hit, but they are only groups of 4-5 mobs. This will easily be dealt with using Hex properly.