This is a VERY personal decision for the couple, and if you're not yet or newly married, it should be part of a series of meetings the two of you have together. Work it like this: the 2 of you make a date for say, 2 weeks from now, with the understanding that you bring all of your financial records to the table for the meeting (prev yr's taxes, pay stubs, credit cards -ALL of them), other debt, retirement info). You sit down w/ the papers/computer screens, and go through it.
If both of you are fiscally responsible, always pay your bills on time, have some savings, then do whatever you both want to do.
If one of you can't remember to pay bills on time, has a big pile of unpaid credit cards, and one of you doesn't, it's important that the one who is more "with it" not freak out, and the one who is less "with it" completely fess up, and the two of you figure out a plan to handle it that will WORK and not upset either party. This was my situation when I got engaged, and the result was basically that I took over the household finances, and gave my DH training wheels for a long time, with a gradual return to normal. I try to keep him in the loop and give more of a full report on where we are about once a quarter, and he has full access to our accounts, but never bothers to look at any of it. This is hilarious to me, because he knows the numbers at work to .01%.
If one person is basically handling the finances, having joint accounts can be a major pain in the *****. If the med student has the good fortune to have a partner who is fiscally organized, I personally recommend having basically all the bills turned over to that partner, so you don't have to worry about remembering to pay the electric bill while your schedule is upside down. This CAN be easier if you have a joint account, but can also be managed with separate accounts, particularly if you just make a transfer to the major payor whenever you get a loan disbursement.
As far as paying back the loans, this once again goes towards what is more impt to the couple -emotion or finance. As long as the payments are being made, it doesn't really matter how or whose money. But if you're a resident living on chump change, and your spouse wants you to pay exactly 50% of the mortgage and expenses, and won't take you along on a vacation in the Bahamas because you can't afford to pay your way, I'd kick him to the curb.
Usually if you lay out the numbers, and say "we'll save $40000 over 10 years if you help and we pay off $x/mo more on this" a sensible person will do it. But $$ can trigger all sorts of emotional responses in people.