Postaed by mauld:
"As far as DL's bucket of seats, it can't be any worse than CO's policy of no seats released prior to 30 days, and non at all released within 72 hrs of flight--so in that regard CO also flys BF with 'empties'."

Actually, Delta's system is better ( at least for Plat's ):BusinessElite Upgrades ( fare bucket Z )are realesed up to 331 days out, and will be immediately confirmed at time of booking, even if months out! If you're flexible with routing/dates you should be able to get these most of the time, even on DL codeshare flights with AF/CZ. You don't have to play the lottery that often, except when you're looking into flights with an 75% BE load and only a week to go. But even in those cases i clear the waitlist for 50% of the flights. Unfortunaly DL does not clear upgrades on the day of departure, but surely closer then 72h out.