These projectors have 720p resolution. Maximum recommended screen diagonal for 720p is your viewing distance divided by 1.3. I sit 8' from the wall, so the maximum recommended screen diagonal is 72". This affects different people in different ways though, so once I get the PJ I'll experient and see just how big I can go without serious image quality degradation.

In one of the above posts I have a mock 72" screen I made out of posterboard. I definetly have the room to go to 92" if I'm satisfied with image quality.

Ambient light is definetly a concern. My room has four huge windows. I'm going to combat this in two ways...

1. Double layered black velvet curtains.
2. A screen with a higher gain reflects light better giving you a brighter image. I plan to order screen samples a week or so before ordering the PJ. Different screen materials play a huge part in your image characteristics.