Alan F;
No they don't. Acupuncturists have no clue as to why their methods work. Furthermore, they only work sometimes and on some people. I know, because my wife had acupuncture treatments from a prominent local practioner and, after a few sessions, nothing whatsoever happened, which leads me to conclude that the little benefit my wife thought she got the first few times was the placebo effect.
Actually, accupunture works (in terms of changing a recipients body chemistry) just as well as 'conventional' drugs;
http://www.csicop.org/si/2003-03/acupuncture.html
New research has replaced this mystical sham medical procedure with a simple evidence-based no-needle treatment that stimulates motor points and nerve junctures and induces gene-expression of neurochemicals and activates brain areas important for healing.
Essentially the old method worked (as in inducing biocemical change by stimulating points on the body). You can do exactly the same thing without needles, using the little conductive plastic discs they use to attach ECGs et. al..
The ancient theory behind it was fanciful and added a lot of bollocks that does nothing, but it does work.
It's just like a Shaman using willow salic to relieve pain would be adding a lot of bollocks (with the rattling stick and chanting) to what we now call Asprin, and have a fanciful theory behind it (the infusion drove the evil spirits out).
Of course, that fact that this research is not yet widely known, and there isn't a massive research effort going into it might have something to do with the fact that drugs are a great way to make money, and developing a virtually zero cost option for certain conditions is not a great way to make money.
I'm sure there are other folk-beliefs that will, upon investigation, turn out to be based on something that does work, or is real, but with a support structure of supersticion and misconception.
Homeopathy is still to be 'proved' (I know anecdotally lots of people feel it doesn;t need proving); if it is, it will be quite a thing; proving acupuncture was just good scientific research methodolgy. Proving homeopathy means you have to show how something that isn't there can effect something; if proved, it would indicate H2O has some property of 'memory', or that somehow the fluid associated with the original additive have retained some active characteristic that we cannot measure at this time.
Here's the above quoted page; it's a great article.