Yes, you still need to bend your elbows, the elbow should be the highest point of your stroke as you pull, however the "S" shape went out of fashion a few years ago. Your hand should point down immediately it enters the water to start the pull, the "straight arm" relates to the forearm, it doesn't mean your whole arm. As you pull back your elbow rises out of the water and you should be able to feel the water pressure on your hand and forearm. Make sure your hand exits the water by your thigh - many swimmers lose quite a lot of their effectiveness by pulling their hand out of the water too early. Watch videos of Rebecca Adlington and notice how she makes herself really long in the water, stretching her leading arm out in front as far as possible as she rolls and following through behind her. And make sure you're not crossing your arm over the midline of your body as you reach forward, that can lose you centimetres. Our tri club coach is constantly scolding my OH for crossing the centre, she says he's a good swimmer but still could be seconds better by not crossing over.