As the 90s progressed, it became harder and harder to cash in the points. Not only were there blackout dates, but airlines started putting tight limits on the number of seats they would release for mileage on each flight. And the number of people with points exploded, so there were more people competing for fewer seats.
Then in the late 90s the mileage requirement per seat started going up. 25,000 miles became 30,000. Then the airlines introduced "dual track" mileage, charging a higher set of miles for "peak" periods - first 40,000 and then 50,000. And these were for flights that you typically wanted to take, so they effectively raised the rates unless you wanted to fly the red-eye.
It looks like the next step is that the airlines are just going to go to 50,000 miles for everything. I just got this from United:
Effective Oct. 16, 2006, the number of miles required to redeem for many Standard and select Saver Awards will change. As an example, the domestic Economy Standard Award redemption amount will increase from 40,000 to 50,000 miles, matching most other U.S. carriers' current standard award levels.
Even Southwest, which had the most liberal and user-friendly rules, is tightening down with one-year expirations on their tickets and certain blackout periods - which they didn't used to have at all.
And during this time the flying experience is getting worse and worse with more packed-in seats, fuller flights, more delays, higher ticket prices, and smaller flight crews. It seems that the airlines should be giving me MORE rewards for flying so much, not less.