There's an editorial in today's "Economist" that gives some facts supporting our worst fear -- that the value of FF miles is heading for a fall. Here's an excerpt from the article:

"Miles outstanding have risen by an average of 20% a year since 1995—two-and-a-half times as fast as the supply of dollars. Central bankers would suffer sleepless nights at such reckless monetary expansion were it not for the fact that they are usually up in first class collecting double or triple miles. The plain truth is that airlines have been printing too much of their currency. They are issuing more miles than they can ever supply in free seats. (Only a small fraction of miles are used to buy other goods and services.) As any first-year economics student knows, excessive monetary growth can lead to hyperinflation and devaluation."