Yes they have!
Pratt and Whitney did a study years ago when they intoduced that greatest peice of junk known as the JT9. (as opposed the the fantastic JT8)
Although an individual takeoff at full thrust will save fuel on that takeoff, the fuel burn will be higher over an average life as the deterioration in engine performance increases.
Cannot remember the numbers exactly but .14% fuel reduction per 1000 cycles was the number mentioned.