I was a non-traditional student (worked as an engineer for 9 years before deciding to take the plunge) and was lucky to get into med school in the US on the first shot at the age of 32. I graduated and have completed two years of residency (one in family medicine, then switched to internal medicine). One of my friends (also an engineer) is currently in the process of applying to med school this cycle and asked for advice, so I visited SDN to see what has changed in the seven years or so since I applied.
Given all that's going on in medicine today and the relative lack of enthusiasm common in residency, it's really refreshing to see the excitement in this forum. As a non-traditional applicant myself that "succeeded" in getting in, though, I thought I would share one piece of advice.
Grades and other measures of academic prowess are important due to the competitive nature of the application process. However, becoming a physician is not about a towering intellect or even a sparkling personality. It is, first and foremost, about persistence and the ability to deal effectively with the HUGE financial sacrifice and time commitment required, particularly in residency. Having gone through it myself, I firmly believe most of you will succeed in getting in, whether it's on your first try or after several attempts. If you want it bad enough and are willing to sacrifice, you will get in.
I only chose to add my two cents after reading some of the great posts about current family / relationship status and other interests outside medicine that some of you have contributed (e.g. doctorold and therainemaiden, to name a couple). All I can say is that, particularly for non-traditional students, you must do your best to become fully informed of the time commitment, family / relationship sacrifices, diminishing financial benefits, etc... involved in the process. I was married and already had one child when I started medical school. I can tell you that it has been a HUGE struggle personally and financially to get where I am. And sadly, if asked whether I would do it again or not, my answer would have to be no.
I am in no way trying to discourage anyone, but I just wanted to stress the importance, for both you and those you care about, of being fully informed of the process. Talk to other non-traditional students at all stages of the process (preclinical years, clinical rotations, interns, residents, and practicing physicians). Read as much as possible about the current state of medicine for practicing physicians and about being an "older" med student / resident (just finished one great book named A Quiet Death, but there are several others out there). All of these conversations and reading will not be a waste. It will not only help you make sure your decision to become a physician is the right one but also serve as great preparation for interviews. (It was my experience that, as an older applicant, interviewers were quite prone to asking about family, past career(s), motivation to change careers, awareness of current state of healthcare policy, etc...)
I really wish all of you the best of luck. Don't be discouraged by the grueling process, but definitely do everything in your power to make sure this is the right decision for you. If you take an honest, well-informed look at the process and still want to move ahead, or if you already have, the good news is that you will very likely get in. Persistence, thick skin, and hard work is all it takes to get there.