I am in my last year of MD/PhD and going into a surgical subspecialty. I have a lot I could talk about but here are some thoughts:
1) It is difficult, but certainly possible to have a successful career as a surgeon scientist. During my time as a student, and also on my interview trail, I met many role models (both MDs and MD/PhDs) who are very successful in both clinical practice and basic research. From what I've seen, there are 2 things that all of the successful surgeon scientists had in common: 1) Have a full-time PhD colleague/subordinate be in charge of the day-to-day operations of your lab. All of the role models I met had a fantastic full-time researcher be in charge of a lot of the mundane but time-consuming tasks of being a PI. This way the surgeon scientist only really needs to worry about writing grants and attending lab meetings. 2) Limit your clinical practice to a small number of surgeries/diseases. For example, I met a surgical oncologist who only operates once a week, but does only one kind of operation. So even though the TOTAL number of operations he performs is relatively small, in that one operation he has one of the highest case volumes in the state.
2) The time commitment required for MD/PhD is no joke, as others say. You are giving up on many years of attending salary. This can really affect your personal life in other unforeseen ways too. I've definitely had to put off having a child with my significant other because of the extended training and low income. Watching the past few Match Days from afar has been a miserable experience also. With that said, now that I'm finally at the end, it's very nice to go into residency not having any loans whatsoever - it will help a lot in getting good mortgage for a house, for example. Also, consider that there are many MD-only students who took years off between undergrad and med school. For example, I know someone who started medical school in his early 30's after working in the restaurant business. He is now a 4th year ENT resident at the age of ~40. Compared to him, I will still finish my training at a younger age, have a PhD degree, and be debt-free.
3) As OrthoTraumaMD said, I don't think you NEED to be a MD/PhD in order to be a good basic researcher. The role models I encountered during med school and on interview trail were about 50:50 split in terms of MDs vs. MD/PhDs. But I think that a lot of the MDs who engage in serious basic research spend a couple of years doing research fellowships to get the required skills (whether it's during medical school, residency, or later), so the difference in "years wasted" may be smaller than you think.
4) I do disagree with OrthoTraumaMD that having a PhD has no beneficial effect on residency applications. In my experience, having a PhD definitely helps you land more interviews at "top" academic institutions - provided you are already a good medical student in the absence of your research experience. If applicant A has great grades from classes/clerkships, stellar Step scores and LORs but no research experience, and applicant B has a PhD and dozens of publications but crappy grades/Steps/LORs, residency programs will pick applicant A 100% of the time - and they should. But all else being equal, having the PhD on top of everything definitely makes you more attractive to academic programs.
I had very good medical school track record, but there was a fair number of other applicants with similar stats as mine. But most of these applicants still had a mix of "top" and "mid-tier" interviews, whereas I was able to fill out all of my 18 or so interviews with just the "top" academic programs. And at many of the interviews I attended, I got very strong feedback from faculty that other candidates didn't (e.g. getting the Department Chair's personal cell phone number, someone telling me that I was only 1 of 2 candidates to get the maximum score on their "application score sheet" and showing it to me as proof, post-interview communications both to myself and my home PD). I think that was primarily because of my PhD and 30+ pubs/abstracts, even though my research has nothing to do with my chosen specialty.
But again, there are other, less time-consuming ways to achieve the same thing. There was one other applicant who I met at basically all of my interviews. This person was a MD-only student who was a lot younger than me. I think the main reasons they were able to land all of the "top" academic interviews were because 1) they had similar medical school stats as me, 2) they had chosen our specialty early in medical school and became very involved, having multiple national leadership positions and becoming very well-connected, and 3) they had extensive experience in health services research. I would certainly NOT do a MD/PhD with the primary goal of making yourself competitive for a good residency program.
As an aside, I think that for me personally, I don't think I would have done as well in my clinical clerkships if I had gone straight through medical school. I think that my PhD years helped me to develop team work skills and maturity that I wouldn't have had otherwise. So that was another benefit of the MD/PhD, for me.
5) Finally, I said the same thing in another thread, but don't worry if the specialty you ultimately decide on has nothing to do with your PhD research. This was the case for me and it didn't hinder me in any way. I was universally told that 1) they value my experience and skill set more than the actual topic of my research, and 2) it's going to be many (7+) years between when I finish my PhD and when I seriously dabble in basic research again during fellowship - by then, the basic science field would have changed so much that whatever I did during my PhD would be very outdated anyway.
