Some interesting comments on an old question. My thoughts:

1. If Delta thinks miles are worth 2.75 cents each, I hope they'll offer to buy my miles at that price.

2. I agree that the value of miles depends on how they will be used by the holder, meaning the amount he/she would have paid for the same travel. In most cases, this can not be measured mathematically, since there is no true comparable for sale by the airlines.

For example, a free Int'l Bus class ticket can't be measured by the "rack rate" price of a Bus ticket for sale because if you spend all that money to buy a ticket, you can fly when you want and change your travel after it starts easily. The award means booking months in advance and changing dates is tough or impossible.

Another example: Int'l Bus using an award to upgrade purchased coach. We all know the pice of lowest upgradable fares have risen dramatically over the past few years. This reduces the value of the upgrade award since you have to pay more to use it, but the increase doesn't lend itself to easy measurement.

At this point I use 1 cent per mile as the value to me.