David, the original hood is very wide to accomodate full frame cameras. Because of that it is not very effective at stopping stray light from hitting the front element. If you have a 1.6x crop DSLR the hood is un-necessarily wide and you could get away with using a narrower (and more effective) hood.
You can get the EW-83DII hood from Canon as a special order, or you could get it from B&H. I haven't ordered mine yet.
nickmak, don't use a hood at all? Lenses should ALWAYS have a hood installed, unless you like the look of flare