(I'm sure the citations for what I reference are elsewhere on this site).

The government is on record as saying that polygraphs are useless (the case was a serviceman who had a polygraph that was favorable to his side, exonerating him, but the government didn't want to let him enter it as evidence).

That is an example where a "passed" polygraph wasn't that impressive to the government.  So in that case, I'd have to say that a passed polygraph doesn't mean much.

It is also statistically proven that "failed" polygraphs happen too frequently through abuse and "false positive" situations.

A failed polygraph is more indicative of somebody who was either gullible, naive or a sucker who was likely conned in to admitting to something that the examiner didn't like.  Skill and cunning on the part of the examiner can cause lines on the chart that would cause a failure or inconcliusive result when interrogating most normal, uninformed subjects.

So, I'd have to say that you are damned if you do, and less damned if you don't.  

A passed polygraph isn't impressive to those already in the system, as they know the polygraph can be beaten and is bogus etc.  A failed polygarph can and will be used against you (not in court; where at least you'd have an appeal).