Financially, my two best recent ones were about 8 cents/mile: BOS-SFO midweek round trip and trans-Atlantic upgrade from discount coach to business class, each worth about $2,000 for 25,000 miles.

Most of my miles go to fly kids and stepkids around the country and across the ocean, though. The financial payoff isn't nearly as high but the emotional rewards are much higher. They appreciate the award tickets, using up so many of my hard-earned miles, more than they would appreciate my simply paying for the flights.