My best was $2000 each for two of us in ATL one spring break weekend a few years ago. 3 VDBs (Friday night, Sat. morning, and Sunday morning) netted us $750, $500, and $750 each. We flew for free for a year on those vouchers in the days of $205 RT transcon fares, and managed to do a couple more VDBs resulting in more vouchers while flying on tix that purchased with Delta's own money.