The J, K, and L keys on the default keyboard are PLAY REVERSE, PAUSE, and PLAY FORWARD respectively. They do quite a bit more than that however, and can really get you speeding through source material, zipping around your sequence and, best of all, trimming faster and more intuitively. Here's what they can do:
 
By hitting "J" or "L" one time, the speed of play is 30fps; press twice, it plays 60fps; three times: 90fps; four times: 150fps; and five times: 240fps. The sound will drop out above 90fps.
 
While pressing the "K" key, ALSO PRESS either the "J" or "K" key and you will be going at 8fps, and for audio you get a slow, rather analogue sounding scrub (as opposed to the stuttering scrub you get using the jog keys).
 
Hold down the "K" key and TAP either the "J" or "L" keys and you will be moving only one frame at a time.
 
The additional beauty here is that all these functions work in Trim Mode.
 
The "J", "K" and "L" keys also work to control a deck when you are in Capture/Digitize Mode.
 
If you are right-handed, experiment with moving these functions from their default positions on J, K and L over to the left side of the keyboard onto the S, D and F keys. This puts the fingers on your left hand closer to the Shift, Control, Option, and Command keys and makes the spacebar really easy to hit with your thumb to perform a loop playback when in Trim Mode. It also makes it faster/easier to type since your left hand is already in place so you don't have to frequently shift position.