I have the same problem. It seems to happen in the same spot of the screen every time, but there's no delay or anything -- it can happen any time, even as soon as I turn my phone on. Sometimes squeezing the phone on the side or the front can make it work a little better, but I think it's a lost cause -- I'll be bringing it back next week. I just hope it'll decide to demonstrate the problem when I show it to the sprint people!