I know I'm a bit late posting on here but.........
For most people the biggest change is going from a CRT to any type of flatscreen. In my case, I went from a 32" CRT to a 42" plasma. I found the difference in SD broadcasts startling. And not in a good way. The thing is, it didn't matter what the source of the Freeview signal was. Neither Sky-sourced nor TV decoder made any difference. What I pretty quickly realised was that a) the Freeview signal was actually pretty rubbish to start with (which I didn't realise when I had CRT TV), and b) watching the same signal on a TV that was actually 40% bigger was bound to look "worse".
Having said that, I agree that you get used to it. However, I do maintain that watching SD broadcasts on plasma is slightly more forgiving than on any LCD. Freeview actually looks better on my 42" Pana plasma than on my 26" JVC Lcd!! What does that tell you? Thankfully my (kitchen) JVC is far enough away that I won't ever be watching it for the "viewing experience". Also motion has until recently been much better handled on CRT than either plasma or LCD. Plasma is better per se, but both technologies are now decnt enough for it not to be an issue as long as you keep off 50Hz LCDs of course.
The other point is, Sky HD is just the best!!! As more HD content becomes available over the air these TVs will exhibit exactly why you bought one in the first place. I have been watching rugby in HD for so long now that I actually can't stand watching it unless it's in HD!! Also if you watch a programme that was filmed in HD and then downgraded for transmission over SD the quality is still very good compared to normal SD programming. Two examples of this are Dragon's Den and Jonathan Ross. HD is arriving and will eventually overtake SD.
BUT, whatever any salesman will tell you, SD will ALWAYS look better on a CRT because they are matched to each other. End of.