Yes, I have experienced this problem myself. I have driven the car several times, including two get umped tours one in Toronto, Canada and one in Munich, Germany. Actually, I spent more time behind the wheel of Model S than in the back seat. I was driving during rainy days and also during sunny days. I spent extensive time just playing with the touchscreen. The UI is perfect, intuitive, easy to learn and logical. That's great, but the reflection is just too strong, especially during sunny days. It's like a mirror. You can see yourself in the touchscreen thus making it harder to see what's on the display. And here you have the evidence:
View attachment 16066
It is like that in reality too. Whoever says it is not, is not saying the truth.
Matte screen protector, I don't think it's a good solution. It will be even harder to see through that. Tesla should offer matte touchscreen as an option for those who don't like the glossy one. Or just make it simple and make only matte touchscreen.