It could be 10% rage and 300% damage if those are the appropriate numbers to use. We provided numbers for some abilities in the preview so that players would get a vague sense of the intent of the ability. We tried to caveat that a lot so that players wouldn’t freak out about the math. Numbers are trivial for us to change — that’s not the challenging part of adding an ability. (Now figure out the right number can be quite challenging).

If the numbers scare you, imagine that we just said the goal of the ability is that when you hit max rage instead of wasting it (like you’d do today), you enter into a state where you do increased damage for increased rage cost so that the rage bar drops, but you aren’t penalized for it. The trick to that design is we also don’t want warriors just doing nothing until they hit 100 rage before they can start having fun. We don’t want you to constantly be worried about trying to get Inner Rage to proc. But we also don’t want you to worry if a string of crits or big incoming damage or something suddenly floods you with rage faster than Heroic Strike / Cleave / Execute can drain it again. It’s a safety valve, but hopefully a fun one, and not something that rarely comes into play. If somehow we nail rage management so tightly that you’re just never near 100 rage, then we’d have to come up with a different ability. I’m not optimistic that will happen given warrior history, but the Cataclysm rage model is pretty radical too. (Source)

[...] It’s not supposed to be a double-edged sword. It’s supposed to let you convert rage into damage at a faster rate when you have too much rage. In your example, you’re going to be doing more damage (and therefore more threat) while its active. In other words, you are going to be doing the exact same thing (rage -> damage) you would be doing if you weren’t at 100 rage. There isn’t a currently a warrior strategy that encourages doing nothing and just building rage, and I don’t see why there would be one in Cataclysm. Maybe if Shield Wall cost 50 rage and you always needed to save some for emergencies, but we’re not going to do that. At most you might need 10 rage for Pummel or Shield Bash, and even in that case Inner Rage doesn’t drain your rage. It would be different if the mechanic was “all your abilities hit harder, but your rage goes to zero for the next 30 sec.” Normally, you should *want* to spend rage. (Source)