I based my decision on screen size taking into consideration what my main use is. I went with 50 inch - after being slightly tempted to go bigger than my old 50 inch PZ.
But for my use - plus distance from the screen - I didn't think 1080p was a good enough resolution for anything above 50 inch. I play a lot of console games and I can't even imagine what some of the poorer looking, and lower resolution games would look like on a 65 inch screen. I think my eyes would bleed if I saw a Wii running through a screen that size
That plus I sit maybe 7 feet away which I think is just the right distance for 50 inch.
It is true though how quickly you become accustomed to a large TV supposedly dominating the living room. When I went to buy a 42 inch set just after the new year, my uncle came along. He had been using a first gen Samsung LCD 32 inch set since the day they were launched here (paid £900 for it! how times change) but when he saw how small the 50 inch sets were in the showroom, he bought one on the spot without telling my aunt. She had always told him he wasn't having a set larger than 32 inch
She didn't believe me when I said she would get used to it. But even she admits that she doesn't notice it anymore when she walks into the living room. Think she would probably have killed him if he had bought a 65inch one though :D