You know what gets me? People who don't hold the chef's knife properly for cutting / chopping. In my opinion, there are more than two ways: one of them I consider right, one I consider okay, and the others I consider "wrong". This is based on techniques I've read about and watched from a variety of sources. I mean, I think I do it right ... and hell, I'm a guy without that much cooking experience. Here's what I consider the right way:

Holding. Take the knife, and hold it halfway up; your index knuckles and thumb should "pinch" the blade near the handle.
The middle finger, not the index finger, is supposed to be against the bolster. (The bolster is that thing that sometimes looks like a finger guard, where the blade and handle meet.) Then wrap your other fingers around the handle.

Reasoning. Holding the knife this way puts your hand a little higher on the knife, closer to the blade. The position gives you more control and balances the knife better for weight.

Cutting / chopping. The main contact point for cutting (green onions, let's say) should be near the middle of the blade, depending on the shape of it, but closer towards the handle. The remainder of the blade (towards the tip) provides leverage and "grounding" for the next cut. I'll elaborate. Slice down in a "pushing" motion, then lift the knife while keeping the tip on the cutting board, and pull back. You want the weight of the knife and the ease of pushing to do the cutting for you, unless you're slicing delicates like sashimi -- then you want the weight of the knife to cut as you pull, but that's a whole different thing then. And you continue, pushing as you cut, hinging the tip and pulling back up. The blade shape should be curved so that this motion is fairly smooth.

Anyway, that's what I consider the right way, but not many people hold it like that ... not even some friends whom I thought were experienced in the kitchen! Is it just me, or does no one really care about that? I've found that correcting the technique has easily doubled my slicing speed and definitely improves accuracy. My current knife is an 8" chef knife from Target (Michael Graves line), which they no longer make in this style. Ideally, I will graduate to a Wusthof 8" chef as a primary tool, but I can't justify it right now.