Gives your Chill effects a chance to grant you the Fingers of Frost effect, which treats your next spells cast as if the target were Frozen. Lasts 15 sec.
Fingers of Frost is a Mage talent in the Frost tree. It causes spells with chill effects such as Frostbolt and Cone of Cold to occasionally grant the Mage a buff that makes their two next spells treat the target as if it were Frozen, but not really freezing it.
For example, if the mage has the buff and casts an Ice Lance, it receives the Frozen bonus and does triple its normal damage.
Being a self-buff and not an actual freeze, this effect works on enemies that are otherwise immune to freezing effects (for instance, raid bosses). This means little in the way of Shatter Combos, though, as the two spells you want to use on the charges are always the higher damage Frostbolts instead of Ice Lances.
Chance to buff
This talent shines when used in conjunction with Shatter, causing the spells to be cast under its influence to have a high chance to critically strike. Taking it improves a Frost Mage's mobility by making him able to cast high-damage Ice Lances on the run.
This talent shares a proc roll with Frostbite, so both talents will always proc at the same time when maxed out. This, while redundant, does still give you the opportunity to root your opponent, run away and cast the Lance within 15 seconds if it seems better to do so, instead of having to break Frostbite.
There have been reports of a phantom third charge being usable due to network latency, but making use of it is not recommendable because the poor Ice Lancecoefficient makes it receive little spell power when compared with Frostbolt due to its instant cast time, making it lag behind in terms of damage with a very modest amount of +spell power gear. This discrepancy is such that casting 60% of a Frostbolt in the Shatter Ice Lance's 1.5 GCD time is better in terms of DPS at average Naxxramas gear level (~1500 spell power).
Patch 3.3.0 (08-Dec-2009): This talent now triggers immediately on casting a spell rather than being delayed until the spell strikes the target.