Arcane Intellect

Prior to its removal in Patch 4.0.1, Arcane Intellect was a mage spell that granted a long-lasting intellect buff to any friendly target. The buff lasted 30 minutes. For high level mages, a related spell called Arcane Brilliance granted the buff to everyone in a party for a longer duration, but had a reagent cost. In Patch 4.0.1, the removal of Arcane Brilliance's reagent cost and reduction of its mana cost made Arcane Intellect obsolete.

Tips and tactics
This spell used to be more expensive, but as of Patch 2.3.0, the mana cost of casting this spell has been reduced. The relatively long duration of this buff allows you to "stagger" your castings. Cast it on yourself, wait 5 minutes; cast on party member 2, wait 5 minutes; cast on party member 3, etc. With the new lower mana costs, the need to stagger this is greatly reduced, however this technique can be used to reduce the "Downtime" associated with buffing the entire party at once.

Higher level mages (Level 56+) can also use the spell Arcane Brilliance to cast an equivalent effect on all party members at once. The duration of the Arcane Brilliance spell is 60 minutes, compared to 30 minutes for Arcane Intellect, however Arcane Brilliance uses more than twice as much mana and requires a reagent. The extra duration is a great help during long instances.

All classes except warrior, death knight and rogue use mana and therefore benefit from the increased mana pool this buff provides.

Intellect increases the rate at which you learn weapon skills. Should you have a friend who is practicing weapon skills, this will help out.