Southwest Airlines introduced ‘Rapid Rewards 2.0’ — their revenue-based program — in 2011. After just two and a half years they devalued their points about 15%, reducing the maximum value you can get out of a point to 1.43 cents.
Then a mere year later they devalued again by introducing a sliding scale of value — sometimes you’d still get 1.43 cents a point in value on their cheapest fares, but sometimes you’d get less. That change went into effect April 17, 2015 after two months’ notice.
Now, a year later, they appear to have devalued again and this time they did it without any notice at all.