Primarily a solo PvE or PvP talent as the only times where you will be hit in grouped PvE are when you generate too much threat on a mob or when you're in range of an enemy's AoE attack.
Past changes
Patch 2.1.0 (22-May-2007):Shadowfury now properly benefits from the Intensity talent.
Patch 1.8.0 (10-Oct-2005): Now reduces chance to be interrupted during cast time of Rain of Fire, Hellfire and Soul Fire spells.