Could you explain what the advantage of 720p support (native upsampling to 1080i) is. This sounds pretty important as far as HDTV goes.

Uh, boy. There are two main ways that HDTV signals are broadcast over the air: 1080i and 720p. Different channels use each one. The former has more scan lines but, like current TV, is interlaced so you get the even lines first, then the odd lines, then the even lines again. 720p has fewer scan lines but no interlacing issues. "Progressive" scanning is what computers tend to output and it's what every computer monitor in the world, as well as any LCD or plasma screen, uses as its native input. On the flip side, "interlace" standards are a whole lot easier to do for cathode ray tubes (TV sets, rear projectors, etc.). It's all a big mess.

That said, the upsampling support may or may not be strictly necessary for you, depending on what sort of HDTV tuner you end up buying. Tony probably knows more about this than me, but I'll bet that some HDTV tuners have this upsampling bulit into them. If you're planning to do over-the-air HDTV receiving right now, then have a look at the feature sets of the different HDTV tuners at the shop where you're buying your Sony. If your main source of video is traditional TV plus DVD, then you don't need the feature.