Ed Schubert has started producing his articles on writing now. Check out his Sideshow Freaks blog for a variety of interesting topics. I particularly liked this point from his article on using metaphors:
Another advantage of using metaphors, similes, and analogies is this: they help people remember your keys points. By using one of these comparative devices, you are subliminally telling people (by placing extra emphasis on it) what your most important points are.
This is a very good point, with the counterpoint being that there are times where you will deliberately be toning down your writing, keeping it simple and free of metaphors, just so when you reach the point you most want the reader to carry away, the sudden elevation of language will have the intended impact. I've read stories where practically every paragraph has some sort of simile in it, and I find such stories almost unreadable. It's like watching a movie where all the extras are in the background waving their arms and shouting "look here!" while the main actors are trying to deliver their dialogue.
Anyway, you can read more of his excellent advice here.