I have a 70 Zerker, it was my first toon...
Zerkers are great tanks.. dont let anyone tell u differently.
If you play them right, they can do dang decent DPS... now nothing like a Swashy, but u can get up there in DPS... of course that is in return for decreased defenses, but that is the beauty of zerker... Its like playing more than one character..
With certain AA trees and equipment... u can go from DPS'r to solid Tank with a few mouse clicks....
For instance.. with STA line AA.. buckler reversal... on offensive stance...
you get in a fight, start losing... dont worry, you ahve 3 temp defensive buffs... switch to a tower shield, defense stance, click your 3 temporary buffs, and you've just gone into Uber tank mode, and can last a while longer..... with decreased DPS of course
but with the right AA... WIS/STA is my choice... u can get the buckler reversal and with WIS tree, u get increase in DPS and you zero out the negatives of the Temp buffs, and of your main stances... so you get no decreases, only increases...
Zerker is a fun class because of the multitude of ways to play them...
As for the tanking side.... u get full defensive mode with tower shield... your temp buffs... etc... u can do enuf damage combined with your tuants, to hold aggro... i held aggro better than any guardian i assisted before. Its all in how you play them... Holding aggro for a tank is essential... with the massive taunts u get by 70 along with the decent DPS u can do, u can hold aggro on just about any mob... (as long as those pesky DPS'rs wait for you to gain it first)