Before getting too concerned about the TV there are a few things you can check and try to help determine if it is the TV.
The blotches that you're seeing, do you see them when you're watching a DVD movie or any other source with darker images?
How do you receive your Broadcast HD signal, cable box, satellite or antenna?
If you have a cable box or satellite system I would suggest check the connection between the set-top box and the TV and evaluate the quality of the cable you're using.