I just purchased a 720p 3LCD projector and 100" screen after researching this quite a bit.
I agree with the other answers. It's hard to watch TV with the room lights on. The colors are all washed out. I find that the color temperature, contrast, and brightness have to be changed. We had family over to watch a football game and had the lights on so it's possible though. It still looked pretty good.
Once the room lights go off, it's really a movie theatre experience and the display calibration can match that predetermined by the video test patterns.
From far away it's awesome and it's great with low ambient light. Up closer with bright images we can notice the texture of the screen (or maybe what's called the screen door effect). Overall, I'd give the system a 9 out of 10.
When I first told my wife about a projector, her expectations of the system were 2 out of 10. When she saw it set it she gave it a 7 out of 10. It would have been higher, but she still didn't like always having to keep the lights out.
All in all, I'm satisfied with it and like the high def resolution on the big screen.