Most people are still under the quaint assumption that you can't be punished for a crime for which you've been acquitted. 

Not true.  In cases where a defendant is convicted of some of the charges against him but acquitted of others, the state can pursue a sentence that includes punishment for the acquitted charges. 

Yes.  You read that correctly.  A recent decision from a U.S. district court in Virginia is unusually candid in pointing out the absurdity of the practice, which is apparently pretty common:

After an eleven-day trial, a jury acquitted defendant Michael Ibanga of all of the drug distribution charges against him and one of the two money laundering charges against him in the Indictment. The single count of which defendant Ibanga was convicted typically would result in a Guidelines custody range of 51 to 63 months. However, the United States demanded that the Court sentence defendant Ibanga based on the alleged drug dealing for which he was acquitted. This increased the Guidelines custody range to 151 to 188 months, a difference of about ten years. …

What could instill more confusion and disrespect than finding out that you will be sentenced to an extra ten years in prison for the alleged crimes of which you were acquitted? The law would have gone from something venerable and respected to a farce and a sham.

From the public’s perspective, most people would be shocked to find out that even United States citizens can be (and routinely are) punished for crimes of which they were acquitted.

The opinion itself is refreshingly abrupt and scathing, and seems to have come from the pen of a pretty fed-up judge.  It includes a history of the right to a jury trial, and quotes from Dickens.

As Cato's Tim Lynch explains, extra jail time for acquitted charges both encourages prosecutors to over-charge defendants, and encourages defendants to accept plea bargains -- knowing that at trial they could well be sentenced for crimes they didn't commit.

If you're wondering if all of this is a violation of the Sixth Amendment, well, if the Sixth Amendment means anything at all, it most certainly is.   But we're talking mostly about drug crimes, here -- where the Bill of Rights doesn't apply.