Yeah, you have to have the room for it. Mine is about 10' from my viewing spot and does wonderfully for me. buddy of mine has an 82" DLP sitting about the same distance and I feel overwhelmed when I try watching it.
I think the 650 series has gotten better PQ reviews than the 700 and 800 series, better blacks too. Plus the quattron can really do funky stuff with color.
I got the 65" 8000 series Samsung and even the plasma lovers in the family have liked the set. If I could have justified it I would have gone for the 75" but it would have doubled the price.