Screen door effect is a different thing...
Pixelation is sometimes referred to as blocking, I believe. Screen door effect is something entirely different and is present (really) only on rear projection HDTVs.
My brother owns a Rear Projection LCD and I have an LCD HDTV. Now I know what people are talking about exactly when they say screen door effect. It's a percieved texture of a rear projection LCD screen (maybe DLP as well) which makes it look like you're watching a TV through a barely visible mosquito net, because the space between pixels is more apperent than on other technologies.
It's not nearly as bad as some people see it but it is a matter of perception.
A good example of a pixelation, on the other hand, would be a low resolution DivX movie, where you see the image starts to look like a jigsaw puzzle in fast motion.
What I have seen on my HDTV, is no where near as pronounced as on a low quality digital video. What is important to me, however, is a clear understanding on whether this is a limitation of a television set or a problem with the signal quality.
If you're a streaming a video through internet connection and some packets are lost, you will likely experience blocking of the image until the stream quality is restored.
I have seen opinions on the web claiming that this is a limitation of the video compression combined with a signal quality while other claim it's the TV.
Is this is a signal quality issue, it's not a problem as it will be improved as the TV world moves towards digital and HDTV. If this is a TV problem and I will see the pixelation even when watching Blue Ray, well that really sucks.
Technical knowledge on this anyone?