From http://www.emdria.org/general/custom.asp?page=119: "EMDR seems to have a direct effect on the way that the brain processes information. Normal information processing is resumed, so following a successful EMDR session, a person no longer relives the images, sounds, and feelings when the event is brought to mind. You still remember what happened, but it is less upsetting. Many types of therapy have similar goals. However, EMDR appears to be similar to what occurs naturally during dreaming or REM (rapid eye movement) sleep. Therefore, EMDR can be thought of as a physiologically based therapy that helps a person see disturbing material in a new and less distressing way."
I have found this to be true for me. I used a light bar and headphones with an audible beat. Some people use a light bar and percussion. My therapist elicited a negative experience from my past then took me through specific steps until my reaction to the same stimulus changed. I have found that the negative self-talk and sense of worthlessness is gone; completely. It's difficult to describe and is different for every person depending on their experience. I can't stress enough just reading what the research has to say about it on the web.

I was highly skeptical of EMDR until I tried it. It is a great way of processing troubling issues and gaining control over them.