Attached Link: http://www.hdm-stuttgart.de/~sw19/files/eulerquat.swf

One thing before this gets into a wrong direction: Euler angles are not bad by definition, and in character animation, chances are you want to use Eulers over Quats. Why? The problem that Quaternions have is that when interpolating rotations, it always takes the shortest and direct way and does not give you any way to preset a preferred direction the rotation should take.

I made a small movie clip to show the difference between Euler and quaternion rotation:
Both arms have only two keyframes, no rotation in frame 0 and 90 degree bend and 90 degree twist in frame 30. The Euler rotation is what you would expect: In frame 16, both bend and twist are at 47 degrees. However, in the quat interpolation, twist and bend are both at 34 degrees and front/back is at 18 degrees. I never told the program to rotate front/back, but quaternions make it do that. This is why, despite all the problems, you most probably want Euler angles in character animation - your paramters are not anonymous and interchangeable xyz any more but bend and twist.