I used optoisolators in the camera trigger I built, and haven't had any problems hardware-wise. (I was looking on SparkFun for the components, and found both what I needed and a circuit schematic for what I had to build.) It must have taken a few tens of thousands of shots without issue. (Timelapses are camera-hungry!)
There's the advantage that, as the name suggests, the cable is completely electrically isolated from the Arduino, so there's no chance of damaging either the Arduino or the camera with weirdness.