I'm sorry to hear about the replacement developing problems too. I ordered 2 PW's for myself and my mom and am worried we might get defective ones as well. It's going to be hard to request replacements as they'll have to be sent overseas, and we've already disposed of our old Kindles (a Touch for me and a KK for her).
Did you order replacements for the replacements again? I hope you finally get good ones. No matter how good Amazon is about replacements, the process of requesting for them must be so time-consuming, not to mention frustrating.