Delta is running a summer promotion (no registration required) where you can get a 50% mileage discount when you use your miles for a BusinessElite upgrade. You must purchase a Y, B, or M fare in order to be eligible.
A normal upgrade from US to Tokyo costing 25,000 miles for example would only be 12,500 during the promotion.
The purchase and travel must happen before August 31, 2011. Use promotion code 97020524.
Thanks to Sice for the tip
Are there any good ‘M’ fares out there that would make this worthwile? Full economy (Y & B) fares seem to be higher than discounted biz fares.