No regrets so far. Some of the posts in this thread are a little bit over the top - you're going to be working long shitty hours no matter what career you pick while you're junior. The situation improves when you're senior. This advice can be applied to law, engineering, whatever.
I'd like to caution all the young med hopefuls that these anecdotes are all over the internet and are sometimes just due to a vocal minority. The vast majority of doctors I've spoken to (ranging from interns to consultants) are completely satisfied with their career choice, but I'm aware of plenty that are also not happy with it. You'll find this is the case for a lot of careers.
Agree with Bearman.
Internship is usually the most difficult, as all doctors need to go through the same rotations (which they might dislike), there is a lot of new responsibility, the working hospital environment takes time to get used to, and they have to get used to thinking about medicine in a more practical way. By second year, doctors can already choose to enter as trainees for some specialties (ie internal medicine, pathology, psychiatry). By fourth year, most other specialties become easier to join. Some postpone their careers to travel/have family and do locum work (high pay 'fill in' doctor type of work). By whatever reason (ie too competitive to get in), some doctors are 'delayed' a few years. Specifically for surgery, the hours are tough in the years to follow with no guarantee for a training spot - most cynicism probably comes from this stream. In a non-clinical setting, there is also research, public health, health administration.
Different health services also have different cultures. Some will be more loyal to their employees, others will always try to recruit only the best. I hear some will expect you to work unpaid hours, but most will roster overtime. Junior doctors stay back for a number of reasons including dealing with a sick patient on the ward, finishing ward round/clinic/theatre late, waiting to hand information about their patients to evening/night staff, preparing for the next day or for educational reasons. I would say that doctors finish later a lot more than they finish earlier. As Bearman, says it could be like any other job (I have nothing to compare to).
Working length is also dependent on rotation. Surgical rotations usually end up having longer hours. Psychiatry is pretty cruisy. ED is shift work, but is intense due to the constant patient load. Barring rotation differences, non-trainees work the same amount as interns (otherwise Bearman has a good handle of the numbers).
I would say that clinical specialties including ED, GP, pathology, psychiatry seem to offer the most work-life balance throughout training and consultancy. I wouldn't say that you could pick any speciality and expect to have a good work-life balance. It can be a job or a life undertaking. It all depends on you.