adding...
I've read elsewhere some time ago that upconverting from progressive is easier than upconverting from interlaced. Not sure why that would be.
That said, last night I set my daytime TV to 720P so far can't see any difference. I do use a 32 or 34 inch vizio (can't remember the size) and I can still easily read the vanity card on Big Bang Theory shows ending credits that is in very small print.