Careful Aim is a talent in the Marksmanship tree for Hunters. It increases the hunter's ranged attack power by an amount equal to a percentage of his total intellect. There are 3 ranks.
Rank
% of Intellect
1
33
2
66
3
100
The talent was recently changed in Patch 3.0.2. Previously, it increased ranged attack power by 15/30/45% of your total intellect.