Differences (some of them):
DOs take one extra required class that is not required of MDs.
DOs are allowed to apply to MD residencies, as well as, DO residencies. MDs cannot enter into a DO residency.
DOs take the COMLEX. And have the option of taking the USMLE as well. MDs take the USMLE, not the COMLEX.
Most, if not all, MD schools require a higher GPA and MCAT score than DO schools.
Most, but not all, MD schools average all grades, while most DO schools have grade replacement policies.
In my personal experience, DO admissions offices answer the phone more frequently and seemed happy to help, as opposed to just willing to.
When I called, MD admissions offices, most of the time I got an answering machine saying to check their website and email them because they were too busy to answer, and if someone did answer they couldn't wait for me to hang up. The most decent MD admissions office I spoke with was UCSF Medical. They were efficient, yet also pleasant to work with.
There are some areas of the country with mainly MDs like Boston Proper. (I looked into the likelihood of getting a residency and career in Boston Proper, if I were to go the DO route because I really like some DO schools (their missions, etc.). Results here sum up my findings:
http://forums.studentdoctor.net/showthread.php?t=1015009&highlight=boston )
A very common, yet possibly offensive, assumption is that the
only reason anyone would ever become a DO is an inability to get into an MD program. Ergo, all MDs must be smarter than every last DO.