Well, I think you aren't the only one. However, I won't worry much. I have my fingers crossed for the September 9th event. The moment they update my iPhone and Mac to the latest software, I can peacefully worry about the purchase of the new iPhone.
Apparently it happened with DP5 and/or Beta 2. Do not adjust your TV. Apple will correct it. It is not a problem with your computer or hard drive. There are many reports of this across the inter-webs. Just report it to Apple, and ignore the screen for now.