Dude, don't listen to people who automatically tell you to make your films widescreen. Widescreen for its own sake is pretty awful to behold, and there are some great films out there that do quite well with 4:3.
It is true, though, that a 16:9 aspect ratio can be a lot more useful if you're really trying to work with composition. I might also add that it saves you some bricks, since your sets don't have to be as high.
In short, you should use widescreen consciously. Some animating programs have an option to put a widescreen mask over the image so you can see what it will look like; I highly recommend this.