Even at 6ft it still has a great picture. The only thing is, at that distance, I can see the fine lines across the screen between the pixels. Other people in my house don't seem to notice it and think I'm crazy. I really only notice it if there is alot of white or bright scenes.
I noticed one other person in this thread talking about it as well.
The further away you are you can't really see a difference between 1080 and 720.
I bought a 1080p lcd tv and returned it to get the 720p 51d490
The colors and picture are much better on this tv even with the lower resolution.
It's actually a little better then 720p which is 1280x720. The 51d490 is 1366x768
One other thing you might want to consider is this tv is very glossy. If you are in a room with alot of light you will get bad glare. It's almost like a mirror.
The 51d8000 the screen isn't as reflective. However I have seen people complaining about the anti glare film on the 51d8000 screen peeling off.
Good luck deciding I know its a tough decision. The tv does look great but of course 1080p is better.If you do go with the 51d490 you can get a few pairs of 3D glasses with the money you saved.