The snare effect is useful for avoiding fighting aggressive mobs you would rather run past, assuming of course they don't resist each time they attack. On foot, a chasing creature will likely get in 2 or 3 hits on the mage (some creatures run faster and swing faster than others) before you outpace them. Mounted characters will usually be hit a single time before getting away.
Now a passive effect and is available only to Frost mages.
Now grants an 8% chance to Multistrike instead of 7% Haste.
Hotfix (2012-09-18):Frost Armor now increases spell haste by 7% (up from 5%).
Patch 5.0.4 (2012-08-28): Frost Armor has been redesigned. Now increases spell haste by 5%. Frost Armor no longer reduces physical damage taken and the [Chilled] proc does not reduce attack speed. In addition, there is now a 3-second cast time. Frost Armor no longer has a duration and will persist through death.
Patch 2.4.3 (2008-07-15): No longer a magic effect and cannot be dispelled.
Patch 1.12.0 (2006-08-22): Chilled effect: Due to the haste effect change, the tooltip has been changed to 25%.
Patch 1.8.0 (2005-10-10): Fixed a bug where the Chilled effect caused by Ice Armor/Frost Armor was not removed properly when shapeshifting.
Patch 1.6.0 (2005-07-12): Targets that are immune to movement slowing effects will no longer be affected by the Chill's movement slowing effect. Targets will still have their melee attack speed reduced.