To answer some questions about the berserking enchant:
1) Its proc rate is about the same percent as mongoose (at least once a minute with the chance to double-proc and refresh itself)
and
2) It should never to be the ideal enchant for feral tanks due to the drastic drop in armor (25% to total value)
In my guild, I dps in our 25 man runs since we have an overflow of tanks and I am wearing 5 pieces of the Heroic T-7 gear, so when everything on bosses goes off, I am usually sitting around 53-56% crit for my shreds, white attacks, and the occasional mangle. Since I have 2 more special abilities that don't have a crit chance and are only affected by boosts in ap, this enchant is wonderful as its an overall boost in damages done in my opinion. Sine mongoose still gives us the +120 agility and the attack speed bonus, its great for tanks and i would suggest this for any feral dps who is running in gear prior to the stats of the T-7 gear. But after you gain a certain amount of crit, its a good idea to get the massacre enchant or spend the cash on berserking enchant since the raw ap affects all your output as opposed to just half of them.