A Frenzied Berserker is a huge issue, but I don't see it as unavoidably negative as people here seem to suggest. The deathless frenzy has the same drawbacks as the Diehard feat (which the FB gains as a bonus), namely that he'll always die. I played through Against the Giants in a group with an FB, and the DM played the giants somewhat strategically, essentially taking all the monsters in the adventure and setting up an ambush in one large room once they became aware of our assault. Once damage was done, the FB flipped out and charged in. Sure, he didn't "go down" until his frenzy ended, but he was at something like -756 HP after the few rounds that they were still attacking him, and hadn't killed everything (though I think he one-shotted the Frost Giant Jarl with a full-Power-Attack crit from his scythe). It's pretty draining on party resources (and the FB's experience level) to be resurrected time after time. There are tense moments when you're trying to immobilize the FB while healing him to the point where he won't die when his Frenzy ends.
The FB is a huge upside, huge downside character. He's not overpowered in a guaranteed win sense. Our characters understood that the FB made them a completely ridiculous fighting force, but that there was great risk involved. A lot of the party was devoted to "managing" the FB, but we all knew that going in and we had fun with it. Yeah, he might kill everyone, but if all the players understand that, it can be a total blast.
I think full disclosure is the best way to go about it. If the other players don't want an FB, then no player should make one, but that's no different than any other situation where one player wants to do things that other players don't want to do. But if they know what they're getting into, then everyone can have fun.
As far as tips go: calm emotions and grease are important, and we had a Paladin who just jacked up his AC as much as possible and would throw himself in front of the Berserker if the FB made his save to resist calm emotions. The FB couldn't one-shot him unless he rolled consecutive 20s, so he wasn't that worried. It was kind of a neat role-playing "solution" to the problem -- the Paladin played the "over-the-top hero" angle, valiantly risking his own life to save the party, and it also had the excitement of the risk of death. If you want to min/max the FB even more, taking one level of Warblade (Tome of Battle) at CL 9 allows him to take Iron Heart Surge, which would presumably end a Frenzy. Customer Service recently ruled that you can use any maneuvers in a rage, provided the maneuver doesn't require a Concentration check.
I'm Cleo!
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