I think there is a confusion between two views of acupuncture. First as a way of stimulating the nerves, which puts it in the same class as TENS (which may be a placebo as someone said, or may be a valid treatment as Steve said). Second there is the woo aspect.
There is no excuse for modern acupuncturists to talk about Qi and meridians, since these manifestly do not exist, but in the context of medical knowledge at the time it was invented they are probably as good a guess as could be expected. For all its errors, the meridian diagram looks superficially like a diagram of the nervous system, and not completely ridiculous considering there was none of the knowledge we have now about how nerves work.
The problem with acupuncture as practised in alt. med. is the refusal to update our understanding of how stimulation with needles could have an effect, just like any other nerve stimulation, and the insistence on regarding it as some sort of lost ancient wisdom which can only be understood in terms of the knowledge of the time.
