I have a friend who works for a government accounting firm out of northern virginia.

When he was taking his 5-hour long polygraph test, he admitted that he had smoked marijuana, and they asked him if he has ever smoked more then either 17 or 21 (can't remember which) individual times. He said no, passed the test, and afterwards asked why the number of times mattered. His instructor said that the government, through testing, determined that any drug act done at least 17 (or 21) times is considered a habit, and will result being an unacceptable candidate for any government position.