This is the skateboard footage provided by Dan. I think it works well. I prefer using the optical flow option. It seems the most fluid and polished. The others seem like they might be best if you're doing something stylized.

This is footage of some paint dropping into water.

This is footage of raindrops hitting the ground. I don't think it works. I had to slow it down so much to get it to loom fluid, that you can barely tell it's moving at all. Probably would work if the footage was shot at a higher frame rate.