I have got a Sony 46" XBR and would like to share some experiences, running it with MCE 2005 and Vista Media Center .
First thing - it is huge. I have miscalculated its size. It was looking smaller in stadium-like showroom, but in my lounge room it is all totally different matter. I am believer in "bigger is better" so no problems here

But be aware of the fact that it will look much bigger in your room.
It is not as slim as I thought it would be. My former 42" plasma was slimmer. But it is no rear projection so it is just a matter of some extra centimeters.
It is heavy - 38kg. I have no idea how, monitors are getting lighter every year. But it is not that I need to lift it every day.
After happy unpacking and heavy lifting it was ready to be connected and switched on. I have decided to try built-in tuner and speakers first.
Auto tuning was a quick affair but picture had to be adjusted, from default horrific "Vivid" to "Standard" and some color reduction.
I was generally satisfied with the picture quality, but it was much better looking on HD channels. It was not that obvious on my previous 720p TV.
Sound quality of built-in speakers was as crappy as I suspected it would be, so no miracles here.
Then I have connected it to my 2005 MCE with 1650 Pro ATI card via DVI/HDMI cable. 1080p was not a problem with 50Hz. No overscan as TV have sensed PC connection and switched on 1:1 pixel mapping. Desktop and MCE interface looking flawless.
TV quality is better than on built-in tuner. After some more picture adjusting I was happy. So have decided to put BD disk in. It is X-Men III. I had PowerDVD BD edition installed, but no luck here. The picture got wobbly and message appeared that HDCP is giving me the finger

I have expected this from reading some posts here, therefore had a Palit 9600 GT Sonic ready to take it's place. I was expecting it to be noisy, but I was wrong - it is very quiet.
I have removed Catalyst and installed latest WHQL Forceware driver. 1080p - no problems, no overscan. Picture is crispier somehow, or it is an illusion. TV PQ is better IMO as well, but now I was ready to watch my first BD. Prior to BD expirience I have decided to watch XMen III on DVD. Now it was a BD time.
It is really good, I had a reference to compare and happy that have spent my money well.
This TV is built for 1080p, and motion compensation(100HZ) is working well, as I have latest F1 race in 1080 mkv and it looks majestic. I have even watched some of that game which mistakenly called football

and it was looking good (visually

) I think that any NRL/AFL fan will love it
I am happy with this TV in pair with 2005 and think that it is a good choice for HTPC user.
Tomorrow I will dual-boot it with Vista and post here my experiences.