In the Burning Crusade its icon was changed from blue to gold.
For every level gained, the AP reduction for both Roar and the warrior's Shout increases by 1, making both skills equivalent at level 80, with a reduction value of 411. (This undocumented change was likely made in Patch 3.0)
Neither [Curse of Weakness], [Demoralizing Shout], [Vindication], nor Demoralizing Roar stack. The curse is superior with no talents involved, but comes at the expense of the warlock not being able to cast [Agony] or [Elements], decreasing damage output. When fully talented, both Roar and Shout reduce AP by 575, while the curse and Vindication 'only' reduce it by 574.
Tips and Tactics
Use this early on in the battle to lower the enemy's attack power.
It's especially useful when you're being attacked by multiple enemies.