Go to my gallery and read the article about neck irritation. It pulls together all the things everyone's been saying.

The skin on the neck seems to be the most sensitive, so you need to be diligent about stretching it flat. Be careful bout not applying too much pressure to the razor and keep the razor angle as flat as you can. Don't shave too aggressively. Don't try to shave off too much at one time. And when you finally get down to skin lighten up on the pressure some more so you don't shave off a fine layer of skin.