As Paul Overton puts it grandly "For centuries, man has been looking for a way to go sledding without all the pesky exercise, and Josh has found it!" Indeed he has. Josh of Cycle Karts rigged a winch to a 8 hp go kart engine so that people could sled down be hauled back without any strain:
The final winch set up involves an 2100 foot long rope that is spliced and will run all day long in a continual 1050 foot loop. The rope alone weighs 70+ pounds and the winch without the rope is close to 200 pounds.
The three different shafts and accompanying gears result in a final drive ratio of 30:1-4.5:1 so it is capable of pulling three adults up a 30 degree incline at comfortable slow speeds or a rather bumpy high speed.[...]
Note the mountain bike grip shift toward the top of the picture, which is our five speed throttle control. Also barely visible in this picture are the three pulleys that keep the line from jumping as the line makes 4 passes around the spool before heading back down the hill.
There's a video of the winch in action at the link.
Link via DudeCraft
Admittedly, it's a much bigger hill.