I don't know that I would recommend a puppy to a pre-med who didn't already have a dog. Puppies need an awful lot of time and can become seriously neurotic if constantly left alone for long periods of time. Also, remember that we're going to be poor - my dog would chew anything in sight but it was my $150 Cole-Hahns that she actually *ate*. My dog, despite my best efforts, probably destroyed at least $1,000 worth of property as a puppy. Cats tolerate alone time much better.
Having said all that, though, this is a great topic! I have a 3-year old German Shepherd that I got when she was about 7 months old. She had been raised by an older woman who was an "animal collector" - had 30 dogs before she called for help. My dog was the bottom of the pack and so poorly socialized with people that they considered putting her down. She was not fond of women and probably not a good choice for children.
Enter a single man - me! My dog and I are about as close as two creatures can be - shepherds tend to be one-person dogs anyway. When I talk about med school, I'm often asked if I'm giving the dog away. To me, lifetime commitment means just that. My poor dog, whom I got before I decided I could no longer run away from studying medicine, has already adjusted to long periods alone during my pre-reqs after work each day. But I walk her as often as possible and we have a lot of fun for a couple of hours every evening. I love it when she lays on the bed next to me, trying to "read" the same book I'm studying. It's not an ideal situation, but she would (in my opinion) be hurt far worse by losing the only real home she's ever known.
The dog is a factor in my school decision (assuming I get >1 offers). In Oklahoma, I can probably rent a house with a small yard pretty cheap. She likes staying outside and it's not a problem. Heaven help me if I have to get an apartment with a 70-pound dog. I don't know what we'll do, but we'll manage somehow. She's my fur-kid!!!