The Listen skill enables you to detect sneaking enemies. Normally, sneaking enemies are invisible until they attack or take a similar offensive action. The Listen check is opposed to the enemies' Move Silently check. If your result is higher, you can see the sneaking enemy as a transparent, gray shape with small, red bursts occurring where their feet would be.
Because it is currently not working properly it is not possible to use the listen skill to detect enemies while you are a blind which takes much away from the usefulness of this skill.