These nasty monsters patrol a fair distance. They hit fairly hard and do an AoE fear (Agro reset), an AoE knockback, enrage at 50% and an AoE thunderclap. Watch to make sure your back is not facing another group or a cliff edge. After the AoE fear, most melee will lose aggro and the berserker will go for the ranged damage or a healer, so keep an eye open.
These things take a tremendous amount of space to fight, do not risk fighting them near other groups. The main problem with these is that they A) do a ton of damage, around 500dps to plate and B) wipe aggro on everyone near them. This means that there is a very high risk of the zerker wiping threat, jaunting off to kill a mage, and then being taunted. Elimintating deaths on these things is tough. There are two ways to do it:
The Catcher Strategy
Basically, this involves treating the zerker like the spider boss. Have the MT grab the zerker, and have the 'Catcher' stand with the ranged dps. When the zerker sheds aggro, and he will, the catcher taunts him and moves him away from the group as well as possible. The former MT then runs to stand with the ranged dps and become the new Catcher. This strategy is somewhat time limited, because if the tank gets the movement debuff that the thunder clap does, moving him out of the ranged dps will become difficult. With good dps though, you will only need to make one or two transitions.
The Rajaxx Treatment
Named after General Rajaxx of AQ20, this strategy is a bit more desperate, but actually works quite well in my experience. The idea is that since one tank has a hard time controlling these, spread the duty around. Tell your warriors to make sure they have at least quasi-tanking gear on. Then, once the combat starts, tell every warrior to try and keep it off every other player. Every warrior becomes the MT this way. The zerker's dps is really spread out between the tanks so they need little healing, and inevitably, even with the knockback and fear, there is a warrior in position to taunt and pick up the aggro.