It all depends on the projector, and ambient light in the room. I run an Infocus IN72 with both DVD's and Comcast TV. I have 2 windows in the room with blinds that are within about 10' of the screen, and another window about 20' back with an open vertical blind, and in daylight, with the 2 closer windows having the blinds closed I get a very decent watchable screen. At night, it is better, but daylight is doable.
I will Never go back to a standard TV, and replaced a Dual Tuner 57" Sony with the PJ, Even the wife agrees that we should have done this long ago. Light control is a must, but if you can control that, regular TV is just fine with certain PJ's.
I have read that alot of the 720P and up PJ's have a problem with TV viewing, which is why I picked the IN72, and will never look back, it is great, IMHO. I watch a 90" home made screen with Behr Ultra Pure White paint, (upw), and a coat of Matte Urethane. Just couldn't be happier here
Larry