I agree -- as a *gulp* corproate tax accountant, I would not recommend taking a deduction for the air miles.
A while back the IRS tried to tax the value of the FF miles a person received. They chose instead to tax the companies that purchase bulk miles (Credit Card companies, Car Rental Companies etc...). This prevented individuals from picking up income on the FF miles. If individual were required to recognize income on their FF miles, I would agree that if you donated them you would be able to take a deduction. However, dont pay tax on them -- cant get a deduct.
This could be compared to the issue that when you volunteer for a charity you cannot take a deduction for your time -- just your milage to and from the charity.
--Jim
P.S. Any tax related comments I make are for your information only any cannot be relied upon for any tax filing positions. Please consult your own tax advisor to discuss your specific situation with him or her. Also, I will not answer any personal tax questions sent to me via e-mail or posted online.