You also need to care about velocity when using splines as trajectories. In general, if you sample a spline at a constant delta-t, your speed through the world won't be constant.

This is especially true if you've got large smooth curves with small "sharp" curves that you want to keep a constant speed over. You can mostly just ignore it if all of your curves have a fairly constant curvature, but obviously test first.

I did end up using Hermite curves and letting the designers and animators tune it how they wanted.