I came across this question on another forum and thought it was interesting.
See this video:
2 pointer or 3 pointer? - YouTube
Side A argues that it is a 3-point shot. They say that he is essentially shooting a one-footed shot. If you stop the video at the right spot, you can see that when he releases, his front foot is in the air, and his back foot is on the ground behind the 3-point line.
Side B argues that it is a 2-point shot. They say that the shot attempt begins when the ball is raised, and that the front foot is clearly on the ground and in front of the line at that point.
Thoughts?