That’s interesting. I am currently deciding between the Panny 42" PX80 and PZ80 (for my parents).
I am leaning slightly towards the PX80 as currently they will be mostly watching SD TV or DVD’s.
I reckon they are going to be keeping the set for quite a while (probably until it breaks). So would it be worth going for the PZ80 as they may want to watch HD in a few years time.
It's not an easy decision as there are lots of variables to take into account. Many people will tell you to go down the 1080p route in order to be 'futureproof', but this is so much rubbish that it makes me want to hurt gerbils. A triumph of marketing over common sense.
HDTV from Sky, Virgin or Freeview (when it comes out) is usually broadcast in 720p and only occasionally broadcast in 1080i, never in 1080p. This is not likely to change as increasing the number of channels increases the revenue of the broadcasters (though subs and advertising) whereas increasing the quality is actually an increase in cost for them. Given there is limited bandwidth available this is only going to go one way. In a similar scenario to DAB radio many broadcasters are actually reducing their broadcast quality as most consumers can't tell the difference.
This means that your TV or your digibox is upscaling, downscaling or deinterlacing in order to produce the image you see. These are very important processes and if done badly can produce judder and artifacts in the picture you see on the screen. Generally speaking digiboxes aren't very good so you are best off relying on your TV to do this but if your TV does a bad job then it doesn't matter how many pixels you've got, it's still going to look rubbish.
SD TV is still going to account for the vast majority of viewing for some time.
Most people under estimate how close they actually sit to the TV, if someone says 6' then I'd say that it's more likely to be around 10'. I actually measured it and I sit 8'6" from a 42" TV in what is a pretty small room. If you want to differentiate between 1080p and 720p then you've got to sit about 6' away from your TV. Unless you are an AV nut (like many here, that's why we are here) your lounge isn't going to be set up solely to focus on the screen; the TV will be a focus point, but it won't be planned for the optimum viewing experience and therefore I doubt that most consumers will get anything like the benefit of 1080p.
Finally, ignoring all the numbers and technologies involved (most of what you read about in the glossy marketing should be turned off anyway to get the most natural picture) the most important thing is that you are happy with the image produced in the long term (this is important; bright shiny images can be nice at first but can actually be tiring to watch). As such the best advice I can give you is to go and demo the models you are interested in at an independent dealer who will let you adjust the image settings and watch a number of different sources (HD & SD) on the screens side by side.
When I went to demo I looked at the 42PX80, 42PZ80, Sony 40X3500 and Kuro 428XD. I really wanted the Sony when I walked in and when I walked out it was between the PX80 and the Kuro as they were best for
me and how / what I watch. The only differentiation was budget.