Quaternions for real-time animation were very poorly understood when I started working with them. The conventional wisdom of the day was that to interpolate quaternions, you had to use something expensive like SLERP, which is what I did at first. But I later discovered with some experimentation that you have many more powerful options. My initial e-mails on the subject are here, along with the original screenshots from my cute little MathVis test harness.
