Initially UC's will screen using GPA/MCAT scores. UCD (at least) treats GPA/MCAT scores equally. Meeting this criteria gets you a secondary. Good letters of rec, interesting responses on the secondaries, along with the personal statement, EC's from your primary app will may get you considered for interview.
For the most part, UCD has been kind to non-traditional applicants. UCD and UCI have less of an interest with research related experiences, but if you have it, then thats always a good thing.
Really, these schools will look for unique individuals to enhance the diversity of their program. The 3rd year class for this year had some interesting people. One guy worked as a party clown to pay his way through college, another guy played the bag pipes. One girl from the class of 2002 played soccer for a year in europe before applying to med school. This is just at UCD. So as you can see, these people with interesting experiences get in. Since this is unique among everyone, this is something we can't measure.
My classmate, who's in the MSTP (or PSTP as they call it here at UCD), got into UCSD, didn't get into UCI. Since She wanted to be an MD/PhD, she went with UCD's program. So a person can get into a "harder" school, and even be rejected from a "lesser school". Of course any accredited US school is great. But in terms of the UC's, ANY UC is hard to get into. People in CA would pay an arm and a leg to get into ANY UC, let alone UCSF, UCLA, UCSD. Being above the GPA/MCAT mean only indicates that you're above average in terms of grades. You will find that interviews will count the most towards getting in. But the trick is getting an interview, and on top of that, being accepted is based on your whole application, and interview. So to guarantee admission (anywhere), you will need to be above average in EVERY aspect, not strong in one, and medium strength in the other.
Things like letters of recs, EC's, or personal statements can make or destroy you. Depends on who's reading it, and what they are looking for. Again something you can't quantify. I believe one of the non-trads on SDN had some high GPA, and didn't even get a single interview from a UC, despite being a CA resident. Then again, my had a high grad GPA did get interviews. Its not about making a "cut off" in the end, its about having the right combination of things that appeal to the adcoms, and differentiate you from the rest of the pack in more ways than one.
In a nut shell, getting into any US med school is already hard. Getting into ANY UC med school is even harder regardless of something like GPA/MCAT scores alone.
