Crouch sliding is a technique that takes about 1 minute to explain, but its going to be something we will all be developing as long as the game is around. In short, the technique is simply to hit and hold the crouch key just before you land from a jump or bounce pad. As you crouch release the forward key for greater speed. You will notice that if you let up on crouch before you run out of momentum you get an upward surge that is basically a strafe jump. You can hold some pretty amazing speed going into turns or corners with nice control as the movie demonstrates. Note: The video was done by oblivion back in October when the game first came out...so give him the props.
Basic Steps
Jump
hit crouch and release forward just before landing
use strafe and mouse to control direction
let up on crouch key before losing momentum
turn crouch into jump
That's basically it in a nutshell, though there is much more to it in terms of practical application. This is a very brief description of a movement skill that is very subtle and hard to use effectively in a game situation. Good luck!