Question for you guys. Do the THX and SMPTE maximum viewing distance guidelines apply to HD sources only, or do the same recommendations apply to SD DVD sources that have been upconverted to 720(768)/1080p as well?

Any thoughts about this? Thanks!

AFAIk it applies to commercial theaters, i.e. film.

You'll definitely want to sit farther away in most cases for DVD sources. Good HD sources can look incredible up close though. It also depends on many other things including the display and your viewing preferences. It is not a simple topic.

I saw one chart where it said I should be sitting 20 feet away from my 57" with SD DVD - I couldn't imagine sitting back that far.