This recipe is delicious! I tend to add a spoonful of peanut butter because I love the taste it adds. As another reviewer indicated, the dried shrimp and radish are not required and don't enhance the dish noticeably. I always soak my noodles, not boil them otherwise they will cook into a big lump. You want the noodles to absorb the sauce.
I have been making this almost once a week for the past few years with excellent results. I tweak the recipe just a bit by substituting about 1/2 Tb of Asian chili-garlic sauce for the cayenne and usually omit the dried shrimp and preserved radish (these ingredients do enhance the dish a little, but not necessary to have great tasting Pad Thai). Also, I often substitute thinly sliced chicken breast for the shrimp and a shredded carrot in place of the bean sprouts. Hint: Soak noodles in hot tap water, not boiled or they will turn to mush. To test if the rice noodles have had enough soaking, hold a noodle between your finger and thumb, with your thumb nail press through the noodle until it breaks -- it should break away fairly easily, but should still have some 'tooth' to it. Also, I recommend using Golden Boy brand fish sauce.
I started subscribing to Cooks Illustrated because of this recipe alone. Just follow it step by step and you will end up with a great meal. Leftovers heat up really well, although I eat stone-cold straight from the fridge.