I sit anywhere from 6-10 feet depending on seating and it's fine, SD isn't amazing but it's not bad either - HD looks great and I now actually make a point of watching the HD channels where on my old 32" it was never really worth the hassle. You'll adjust to whatever you get - I go round people's houses with 40" screens now and think "eww, it's tiny I can barely make out the detail", my old 32" is now relegated to the kitchen
Have a projector in the man room - it's about an 8" picture, I then walk into the living room with the 50" and think "eww, it's tiny I can barely make out the detail"... Weight is not a prob on newer screens, I got a wall bracket suitable for 50kg and it's not even remotely stressed - worth noting: Never buy rubbish brackets from Comet etc. - they all cost £100+ for even the most basic ones, I paid £30 for a 50" bracket (almost flat to wall, have to use the side HDMI port now!) from Asda and £20 for the 32" one in the kitchen, much better price and work perfectly (even tilt-able).