As many have pointed out it's the viewing distance that matters, but it also has to be coupled with projected resolution. When I watch a movie I don't want to see scan lines. If you project too large and you are too close you will see those lines. Other than that--the bigger the better in my opinion. Does anyone think IMAX screens are too big for the theater? SGTH did an article on this (distance vs resolution) quite a long time ago, it might be possible to find it in the archives. Just as a point of reference I'm using a 100 inch screen, seated 15 feet away, native resolution is 800x600 (CRT driven with Faroudja DVP220). Hope this helps.
How big is too big?
There has to be some sort of ratio of room size to screen size. I was thinking about getting an 84" screen but realized that it would be WAY TO BIG for the room after drawing it on the wall with chalk. Have any of you put too large of a TV in a too small room, or the other way around?