Okay - and this is going to be my final contribution to this particular thread.
First of all, let's address the question "can anyone tell me what shortcomings in allopathic medicine that osteopathic medicine is supposed to address."
To do that you need to look not at D.O.s and M.D.s today but D.O.s and M.D.s about 150 years ago. At that time many of the M.D.s used medicines that were unproven eg mercury for gonhorrea - completely ineffective, and actually poisonous. A.T. Still disagreed with this approach of using medicines and pills, which at that time had no clinical foundation and, after losing several close family members who he felt died in part due to the "care" they had received he founded osteopathic medicine. This did not use the clinically unproven medicines and was instead based on the interconnectedness of all systems in the body - Dr. Still recognized the body's ability to heal itself and stressed preventive medicine, eating properly, and keeping fit.
Now, back to the present day. D.O. and M.D. practice regimes have converged over the years. Now the differences are laregly in the individuals rather than approach or philosophy.
However, the original question seems to include some kind of attitude that D.O.s need to justify their existence to pre-MeDs. I have posted responses in answer to questions, but I have no interest in "justifying" my belief in D.O. to anyone (and I will point out that I read pre-allo because I am pre-allo - I am not a D.O).
Some of the attitudes exhibited in this thread are extremely perplexing. Some people seem to believe that in medicine the white coated M.D. is some sort of omniscient 'God'. My experience of health care however has been that health care is a team effort. The P.A.s, nurses, M.D.'s and D.O.'s are co-workers. Some people seem to believe that D.O.s go off and practice in some other world, that they will never encounter them. Why don't you stop for a minute and take a look at the faculty listings of some of the top 50 M.D. schools. I have only three brochures on my desk here - Albert Einstein, U.Penn. and Mount Sinai. Did you know that every single one of these have D.O.s on their faculty? What are you going to do when you turn up on the ward and your attending is a D.O.? Wave your MCAT score in his or her face and be sure to speak slowly so they can understand you?
At the end of the day, I want to be the kind of doctor who gives my patients the best care possible. If they have a problem I will use the most effective, least invasive means to help them. The New England Journal of Medicine has published papers about the efficacy of osteopathic techniques for things like low back pain. If I had a pateint with such a complaint I would of course refer them not only to a D.O. but a D.O. with a hopefully a residency in OMM. It works. Doing anything less would not be serving my patients to the best of my ability.
Regarding craniosacral techniques which someone mentioned. It is true that such techniques are currently taught, and yet clinically unproven. However, the D.O. community is making rapid strides in providing a scientific basis for their techniques. They are establishing large research institutes specifically to address such questions and I am sure that as techniques are proven or disproven they will be added or removed from the curricula. At present the techniques certainly do no harm (the physicians mandate after all) as they are invariably used in conjunction with more "traditional approaches" not instead of them. However, how do you think allopathic approaches are discovered. We experiment on our patients. We might not like to put it that way, but it's the truth. We give them unproven drugs in clinical trials and to other people, suffering the same disease, we give placebos. If you want to worry about ethics, start at home.
As far as people not believing that *anyone* would choose D.O. over M.D. I think you are making the mistake of assuming that just because you would never consider such a thing, no one else would. People are individuals. They do many different things for many different reasons, often quite beyond our own comprehension. I cannot understand why anyone would drive without a seat belt. However, a good friend of mine died doing this. I counsel pateints with HIV. Some of them don't take their medications. Some because they "can't remember", some because "taking a pill reminds them they are sick and they don't want to think about it" some because "they listen to their body and they just 'know' when they need the next pill", thus causing themselves to build resistance to the very pill that could have helped them. When an overweight patient comes to you for help, you may tell them "stop eating so much". Maybe for you that would be easy. Maybe for them, food is a substitute for other things in their lives and until you help them with those problems they will not stop abusing food. Or maybe they are 14 and the person you need to work with is the parents because the father insists on fried food every night and the mother cooks it to keep him happy, or or or or or the list goes on and on. You can't assume that everyone will make the same choices you would given the superficial details of their life, or you will be stymied in helping them. First you have to really listen to them and try and understand what the problems are behind the complaint. With one HIV client who didn't like taking pills because they reminded him he was sick, I got him to start a vitamin and mineral supplement regime. He took these at the same time as his pills. It shifted his focus from "sickness" to "health" as that is what he associated the vitamins with. A stupid 'trick' maybe, but that client is now compliant and *healthy*. One success - and all because I didn't just assume he took his pills just because I feel certain I would if I were sick.
I guess, the summary is this - you're about to enter a *profession* and as *professionals* your job is to help - open your minds; grow up.
Nicely put Adam!!! 
