Increases all resistances by X per level and causes all spells you fully resist to restore Y% of your total mana. 1 sec cooldown.
Magic Absorption is a mage talent that increases resistance to all schools, and restores mana each time a spell is resisted.
This talent is most useful to mages that expect to take a lot of magical damage. Aside from the resistance added to all schools, it will restore mana for each full resist. The amount of mana restored is a percentage of the mage's total mana pool, meaning that the talent scales with gear. Pre-expansion, there were quite a few raid encounters that required high amounts of resistance, such as Ragnaros, Vaelastrasz the Corrupt and Viscidus. With the Burning Crusade expansion, there are fewer raid encounters that rely on the entire raid wearing a lot of resist gear, and this talent has become less useful. This could still be somewhat useful in PvP situations.
Although the following should not weigh heavy in any consideration for the talent, it is observed that if you do a run through a low-level instance, you will resist essentially all magic attacks against you, and that will give you significant mana regeneration.
Do take into consideration that this talent grants a lot of resistance at max level, and less resistance gear means more room for DPS gear.
Most mages first choose Arcane Concentration at this tier in the Arcane tree, and take Magic Absorption as filler for later talents in the tree.