I got an Apacs Nano Power 900 (White) about 6 months ago. The shaft was okay at first, but then it got more and more flexible. I don't think the racket was that flexible when I got it. Is it because I hit a high number of frame shots? (aprox. 35%) If another post has this information, please direct me there. Thanks in Advance!
What cooler said is true, I think the quality of the graphite also makes a difference as what I believe is happening is the bonds start breaking on the microscopic level. Not enough to crack the racket but enough to make it more flexible.