I thought I'd give a little advice that I've given before on SDN, but I think it's helpful. If you haven't tried getting a part-time job somewhere in the health arena, do (and do it ASAP)! The more experience you have under your belt, and the exposure of working with physicians that can write you letters of rec. that have some REAL meaning, the better your chances. A physician, who happens to serve on a selection committee, once told me to get a job doing something health-related. This can be working as a phlebotomist ("blood-drawer"), working as a patient-care specialist, or any other odds-and-ends thing Human Resources at your local hospital can give you. I was lucky and landed a job in the Lipid Clinic for a group of cardiologists and CV surgeons (which allowed me to work for, get to know, begin to understand the process, and desire a yearning for medicine). If all you can do is set up shadowing programs with a DO, that's good, but when you shadow one DO, see if he or she can get you in touch with another DO in a different specialty (variety is nice). By the way, working in the ER as a tech offers many advantages, the first of which is being exposed to all kinds of patient-care situations. Hope this helps and best of luck!
-Nathan (UHS-COM '05)