Just the other week I had to remove and then re-install a hanging door in order to move a couch out of a room. Although I had help with the couch, I was left on my own to wrestle the door back into place, with a drill in one hand, as I tried to line up the holes in the hinges (yeah, I probably could have just removed the hinge pins, but I chose to unscrew the hinges from the door frame) to screw them back into place.
Needless to say, it was frustrating endeavor and not one I wish to repeat anytime soon.
Unless, of course, I had a DoorJack. The DoorJack is one of those palm-to-forehead "why didn't I think of that" products. The picture to the left explains it better than words can, but the short of it is: The DoorJack makes installing hanging doors an easy job for the individual. Just rest the door on the jack and use your foot to lift it as much as 1.5 inches to align the hinges properly -- without a fight. The jack lifts up to 240 lbs. and won't scratch up the floor or door like the crowbar method.