Hi guys. I just signed up to let you know that I've been having the same issue. Basically a rectangular dead spot in the middle. Sometimes the spot doubles in size, rarely it disappears. I went to Sprint, they said IF they had the parts in the store, it costs $35 without insurance. Luckily it's still under manufacturer's warranty, so I called HTC and sent it in. A couple of things I hated about HTC; one, they wanted me to pay for shipping. After going back and forth with the rep, I got them to email me a label. IT'S A DEFECT! Not my fault. Second, it seems like they insisted I did the damage to the phone (asked if I dropped it 20 times) even though it's common. Of course I had to go on Craigslist to buy a temporary phone which was a pain.
I'll keep you all posted once I get the phone back
I think my next step is to sell it as soon as I get it and get a Samsung or something.