have just bought a 428XD. All that I can say is ... Believe the hype.
I spent months looking at numerous LCD's and other plasma's and up to purchasing the Pioneer 428XD my selected choice was the Panasonic 42PZ700 (Full HD).
I was fortunate to able to compare both sets side-by-side watching my all time favourite movie Star Wars. Immediately it came apparent that the Pioneer colours were richer, more vibrant with the resultant picture looking fantastic, especially scenes having dark/black backgrounds. I then watched Dreamgirls on Blu-Ray and the skin tone on the Pioneer were so much more natural than the Panny.
Now that I've had the TV for a week, I'm simply loving it.
SD Freeview is good though channel changing is a bit slow.
There are so many options/settings on the Pioneer it is overwhelming however altering the basic colour, brightness etc is easy, fortunately.
I'm hoping to buy a blu-ray and a HD-DVD add-on for my XBOX 360 shortly to ascertain how good HD pictures are.
In a word, the TV definite warrants an audition, if you're looking to buy a new TV. In my opinion, it simply beats Full HD models by some margin of the same screen size.