I got married between 2nd and 3rd year of med school and thought a long time about what to do with my name. I hate hyphenated names because even if it's not 9 syllables wrong, what happens when 2 people with hyphenated names want to get married? Even more confusion. I most likely would have just kept my maiden name, except it's pronounced "rank." Honestly, I just don't really like Dr. Rank. Also, since it's spelled differently, it gets mispronounced all the time, which gets annoying when no one can pronounce my first name either (it's long and weird). My husband on the other hand has a nice, normal last name. But at the same time, I didn't want to get rid of my maiden name, since it's a part of my identity. I also didn't want to get rid of my middle name because I like it and it was my grandmother's name (obvious sentimental value). I ended up merely adding his name to my own, so now I have 4 names: Firstname Middlename Maidenname Hisname. I'll go by Dr. Hisname, but any sort of official documentation, like my license, will have both on it. I'll have to think about what we're going to do when we have children.
As far as changing during med school goes, it's really not that hard. Obviously, women change their name fairly often, so people are used to it. Also, I got married after I took Step 1, but it really wasn't hard to change it for Step 2. You just send in a form which is very easy to find and download. Really, it's the same thing you have to do with pretty much anyone else: credit cards, banks, etc. It's moderately easier if you send in the form before you actually register for the next Step, but not necessary. I did both at the same time.
It's also reasonably common for a woman to use her maiden name professionally and her husband's name socially. Personally, however, I do not want to be called Mrs. Hisname. That's his mother. Until I'm a doctor, it's Ms. Hisname if necessary but I almost always go my first name, even w/ patients since I'm still a student. Once I'm a doctor, it's Dr. Hisname and I admit I'll probably be somewhat picky because medical school is too much hell to go through without any recognition.
I have also heard of both people picking a new name and then both legally changing their name. As a side note, I have also heard of homosexual couples doing the same thing, or legally hyphenating their names.
In the end, do whatever you want, because it will be acceptable in American society.