Can't argue with actual experience... but... such behavior seems to contradict the documentation provided at the bottom of the junk mail settings page, which indicates that:
"The Quarantine Level is the numerical score required to prevent delivery of a message at the server."
Based on that description, I woud have expected that if the quarantine level is set to zero, and the message score is zero that the message would end up quarantined. Sounds like my expectation would be incorrect.
Just curious, I wonder if a zero score is a "special case", or if the quarantine level is really the numerical score above which a message is actually quarantined.