Is there any way to disable Skyrim's Auto-aim with bows?

Solution 1:

Open up Skyrim.ini in your MyGames/Skyrim folder.

Search for [Combat]
Add one or both of the following lines:

f1PArrowTiltUpAngle=0.0
f3PArrowTiltUpAngle=0.0

The first line is for first person. The second line is for third person.

Source: http://www.reddit.com/r/skyrim/comments/m8pv2/bow_auto_aim/c2z1omo

Solution 2:

There is now a mod that disables autoaim.