Adam,
Short grass indeed can be a "hazard".
JES II,
As you know, in modern golf, the only "formal" hazards are bunkers and water hazards. The balance of an architect's "hazard arsenal" is of the "informal" variety. Without these components, conditions, and elements, we would have a very limited box of crayons with which to color our courses and make them unique works of art and interesting obstacle courses.
Furthermore, everyone's definition of these "informal" hazards will vary but we include things like sand hazards that are not "bunkers", barrancas, broken ground, what we call "bumps, contours, undulations and hollows", stone walls, fences, buildings, ruins, trees, out-of-bounds, wind,...anything that can add to the interest and challenge of a golf hole.
This is not meant to be a trick question. Just think about your favorite golf shots on courses you have played around the world and my guess is that they in some way are defined by a hazard. I doubt your favorite or most exciting shot is a three foot putt (though I agree it could be terrifying).
I bring this subject up in part because I recently sat through Bob Randquist's seminar on "Basic Bunker Maintenance" out in Anaheim. It was a sold out session and Bob gave a great course. We both agree that much of modern golf architecture and hazard maintenance is the attempt to "elimnate the hazardous nature" of hazards. Many courses are conditioning away the element of luck and unpredictableness that hazards should employ to the tune of 25% or more of their total average maintenance budget. We also tend to toss the hazards to the sides and out of the line of play which takes much of the interest and excitement out of the game. This is not to imply we should be making our courses harder. We need to be making them more interesting and less one dimensional. It is the role of hazards that add so much excitement and pleasure to the game. Without them it would be a very dull game.