I have a 50" Kuro and I watch it from almost 4 meters/13 feet (eye->screen distance). It is great for normal TV broadcasts, even HD ones. But, when playing a game or for watching Blu-ray I usually push the sofa around 1 meter closer to the TV :p Or simply use my beanbag between sofa and TV.
For 7-8 inch I would recommend a 40-42 inch. But if you are a Blu-ray fan or gamer that plays HD games I would recommend a 46 inch.
With more than that I guess it is too much if you also watch SD content. It's all great -- the more the better -- but for HD content, not for SD, as you lose quality by getting too close to the screen.
If you are 10 feet from TV, then a 50 inch would be nice :) (same as myself when using the beanbag)