[chris (OP)]

Why do golf balls have dimpled surfaces? How does this affect the flight of the ball?

[CPT ArkAngel]

Just a guess: they cause turbulence that will tend to stop the rotation of the ball... ?

[Colin2B]

There are two types of flow around an object, laminar and turbulent.
Laminar flow - smooth layers - has less drag, but the layers can separate and then drag rises very quickly. This drag will typically form on the trailing edge of a ball or wing and eddies form in the gap caused by the separation. The dimples cause turbulence and although turbulent flow has more drag initially it also sticks to the surface better and so is less prone to separation.

[evan_au]

Continuing the line of Colin2B...
The golf ball is hit with a backspin, and the golf ball meets the air with a very different velocity on the top and bottom surfaces.
Like an airplane wing, this gives the golf ball lift.
So a golf ball with dimples can fly farther than a perfectly smooth golf ball.
But the dimples also cause increased drag, so the ball tends to drop more vertically towards the end of its flight (compared to a perfectly smooth ball).
See: http://en.wikipedia.org/wiki/Golf_ball#Aerodynamics