You are misunderstanding DF. It is a feat that grants a frenzied Berserker the same benefits as being under a cleric's Death Ward spell. This means that he/she is immune to:

* Energy Drain
* Negative Energy Damage
* Ability Decreasing Effects
* Death Spells
* Spell-like Abilities and Effects

If your Barbarian has died from other means, he/she will need to be rescuscitated (if possible).

The way it's worded, someone who isn't familiar with pen and paper D&D could very easily be confused and believe it does allow them to keep fighting past the point of "death". This is made worse by the fact that Lorne seems to have such an ability in the campaign, leading people to believe that this is the class feature responsible.

So yeah, it just grants you a bunch of funky immunities. They're still very good immunities, but they won't protect you from regular combat damage.