Why does pouring soda slowly and smoothly seem to keep more of the carbonation?
Because your soda is a supersaturated solution of $\ce{CO}_2$, and such solutions are non-equilibrium and hence unstable. Any physical disturbance (shaking, touching a rough surface, etc.) causes it to emit the gas and return to equilibrium state. Throw in some salt, and you will see a reaction even more vigorous.

Supersaturated solutions of solid compounds exhibit similar behavior, but they are not that easy to come by (I mean, starting from the typical household items). Sugar solution is too viscous, and table salt is no good because its solubility does not depends on temperature all that much, so you can't really supersaturate it.

There is, however, another pretty common example of non-equlibrium state, and that is superheated water. If you pour some bottled water into a clean cup, heat it in a microwave for a while, and then touch it not too gently, it may almost literally explode in your face, so beware.