First of all i did used forum search for Demonic Leap and didn't found anything like this, so if it is a repost, sorry.
Second... i'm not sure if its exploit, but there is nothing mentioned in DL tooltip soo i guess it's atleast clever usage...
Anyway, just trying to contribute.
So... if you use Demonic Leap while jumping it throws you up in the air and resets CD when you land. But if you use DL right before you land, it still throws you up in the air but resets CD (like if you landed) allowing you to use Demonic Leap while in the air. That allows you to do a high jump, so you can get on the bridge on Blade's Edge Arena for example. Maybe useful for exploring in non-flyable zones or something else.
Video Link: http://www.youtube.com/watch?v=wUUTT...1&feature=plcp
[UPDATE] USING DEMONIC LEAP WITHOUT TRIGGERING CD!!!
Basicaly same idea. While running forward, jump and right before you land tap your Demonic Leap keybind twice (as fast as you can, but only TWICE, not more). It will throw you forward BUT will not trigget CD. Wait a second, and repeat.
Video Link: http://www.youtube.com/watch?v=rJsmMJu2zmw&feature=plcp