These guys are pretty amazing. And the nonchalance with which they accomplish each trick shot adds a certain understated humor to this entertaining video. But though the guys seem to be developing a seemingly useless (if highly impressive) skill in their spare time, there's quite a bit of complex science at play. In addition to being a highlight at any party, these are excellent demonstrations of two- and three-dimensional projectile motion, and with just a little bit of quantitative analysis the entire video would make a formidable project for an introductory level college physics class.
For example lets look at the segment where the guy tosses the ball in the cup off of a moving skateboard.