My post will echo a lot of
@mimelim 's. I'm very happy with both my career in surgery and my personal life outside of it. But I think it is important for everyone entering this field to do so with an appropriate understanding of what it entails. Surgery does entail a degree of sacrifice and effort that is rare even in other fields of medicine.
For your residency, you can expect your days to start early and end late. Think in the neighborhood of 4:30 nearly every morning, with a 5:30 or 6:00 alarm clock being considered a rare day of sleeping in. The bigger issue to me always than just the hours themselves though is the sheer unpredictability of them. I can't really estimate when I'm going to get to leave, particularly on a busy service. It's hard to commit to dinners or firm appointments. Regardless of what your family situation is, this will probably be the biggest practical barrier - you can't promise to pick someone up at 5:00 or cook them dinner at 7:00.
Fortunately for me, most of my friends are either in medicine or very understanding. So we end up with a lot of last minute cancelled plans, or a lot of last minute made ones. Days when we get done earlier than anticipated, it's very common for us co-residents to look at each other and go..."beer?"
Intern year will mean lots of call too. Don't forget that for right or wrong, surgeons are the ones basically asking the ACGME for permission to have 24 hr call back.
A key difference between surgery and other fields though is that it doesn't get easier after intern year and in fact in a great many ways it gets harder. For Internal Medicine, I think their intern year is nearly as hard and in some ways more painful than ours, but then after that you have an acute drop in hours and in inpatient months, and an acute rise in ability to delegate. Not the case in surgery - you pretty much go at the same pace/intensity for all five years, and as a chief you end up with a unique level of personal responsibility for your patients/service.
Now this leads me up to something I alluded to before...it's not just the hours, it's the emotional investment and toll. I have a lot of days where when I get home, I have no energy left. None. I sit on my couch, maybe watch 20 minutes of some dumb TV show, and fall asleep. I can have bills to pay, papers to write, a house to clean...doesn't matter. No energy left. The work isn't just about the hours, it's about the level of mental energy you have to expend.
Here's a great thread that has been getting some posts lately in the surgery forum, started by someone considering quitting after less than a year of this. It's just not for everyone:
http://forums.studentdoctor.net/threads/leaving-surgery.1193989/