Cecil (or at least the Mrs. did) got about $1.00 per mile of value from his frequent flier account in
http://www.straightdope.com/classics/a3_136.html (“Why are air fares cheaper if you stay over Saturday night?”).
Pretty darn good!
Actually, rereading the article I discover that he (she) spent about $1.00 for the $1.00 value but, in fact, the miles used for the glorious holiday were not revealed. How many miles did he and the Mrs. need for that “free” trip?
So, how much do the airlines think the programs cost them per mile, how much do they charge those businesses that offer miles as premiums and what do you really think they are worth to the average user of those miles?
Incidentally, I use a factor of 1 to 2 cents per credited mile for my own decisions about what airline to fly on given route, once I have retained nosebleed status for the following year (they really do treat you better!).