Unofficially, you DO get priority boarding (or so I think).

A coworker and I were still General Members... meaning usually Zone 4 boarding. We both applied for the card roughly the same time and started having Zone 2 boarding on a weekly basis. He cancelled his card and when it was removed from his account, he went back to Zone 4. We're both FO now so it doesn't matter to us or most people, but if you don't have medallion status it could help you.