In my opinion having worked with acupuncturists and had many treatments, it is pretty much placebo. The only people who i saw in the clinic who were happy with results were people who were getting treated for things like energy levels, and used acupuncture as part of an ongoing health plan, and these people obviously already had it in their head that it was an effective treatment.
I've had much more success with dry needling, there is a difference. There are many styles of acupuncture but the ones i have experienced generally work far away from the problem, to allow " energy flow" downstream, or sometimes upstream, to the site of the problem. Dry needling will also work far away from the problem at times, but that will be because of the musculature and nerve pathways that might be impacting on the problem.
I have met some really good physiotherapists who are also acupuncturists, who have used needles and certain acu- points effectively, but usually they will be thinking more along the lines of nerves and muscles and less about meridians.
This is just my opinion, take it for what it's worth, but i find most types of acupuncture pretty ineffective for musculoskeletal problems, depending like everything does on the practitioner and their skill.