Focusing on eye, general focusing

[forewer2000]

I read that the best focus point in a face is the eye, if that is sharp everything will be fine.
My problem is that even if I focus on the eye, from five shoots maybe one is sharp with the eye in the focus, the others have some focus somewhere near the eye.
I use nikon d80/ 50mm lens stopped down to 1.8 - 3f. using a singe focal point, fixing on the eye when focusing.
Is this the right technique to shoot, or I need to use some other settings? I see that the camera has multiple focusing point selection feature, but I don't know for what? If I want to focus on something I can prefocus on that, so I never used that multifocal thing.
Any thoughts on this? Thanks!

[OsmosisStudios]

If you're at f/2 or f/2.8, it shouldnt be too difficult to get focus. Are you holding the AF-Lock or a single/servo focus instead of continuous or automatic?

[forewer2000]

I think i'm not using the continuous/automatic mode - only the single/servo focus and I hold the focus with pressing half way down the shutter release. Should I try maybe with the continuous mode? Maybe the subject has little movement after I fix the focus, and this is the reason for the unsharpness. I will try this.

[OsmosisStudios]

Continuous would be BAD as you focus/recompose, the camera would refocus.

Can you supply a full-sized or 100% crop of a particularly bad example?

[forewer2000]

Ok I made an example(I don't have a portait now but this is the same issue). http://dl.dropbox.com/u/3894187/sample.jpg
In both image I focused exactly on the end of the match stick, but If I had the bottle behind the match stick than the focus will be on that bigger surface, not on the stick. This is happen also with the face of someone. The focus is not on the eye but on the face.
Settings: Direct flash, F1.8, Shutter speed:1/60 - 50mm. AF-S. Focus point only on the center.

[OsmosisStudios]

How far away is the match-stick from the front of the lens? In this particular case you may be hitting the minimum focus distance for that lens.