This exploit is for the quest You'll Need a Gryphon - Quest - World of Warcraft in icecrown. it will allow you to get the reward and exp BUT you can still ride the 100% mount around.
Procedure
-pick up the quest
-kill the gryphon rider and loot him to get the reins.
-use the reins and mount up and fly back to quest guy
-hit 1 to deliver the gryphon, it will dismount you and you will now see a "?" above his head BUT the reins are still in your bag.
-talk to the quest turn in guy, select reward but DO NOT complete it
-cast the reins again but with ~.5 sec left complete the quest and BAM you have a nice little mount.
screenshot
by -ßlink-