It is just plain marginal to try to view any technology of TV beyond 45 degrees off center.
This forum has commented on viewing angle frequently. Yes, plasmas have somewhat better viewing angle than LCD & DLP, with DLP being a bit more limiting than LCD.
Most people nowadays realize it's undesirable to have to have the TV mounted high so that even normally seated viewers crane their necks back. At & slightly below ordinary line of sight is more pleasant.
Whenever I look at the specs of the various TV display formats; LCD, Plasma, DLP, etc, I find that not all include viewing angles.
Maybe I'm just weird, but unless you have a very deep living room with a theater type tiered floor, so everyone has a direct-on view of the TV screen, there are going to be viewers to the side of the TV, maybe sitting on the floor below the TV, etc, which means viewing angle is extremely important in a normal living room setting. When I invite people over and we are watching TV, I don't want anyone to not be able to see the full clarity of the picture.
One thing the age-old cathode-ray tube TV format has is excellent viewing angle specs. LCD specs usually include viewing angle, I would guess because LCD provides the best viewing angle of all the HD formats. How do we find out what the viewing angle is on other formats; for instance DLP - before we buy?