I have a Pio 507XD which I got just over a year ago. At the time the Sony X series was a set I considered. I had a demo set up by a specialist AV store in good conditions and the same feeds side by side with the Pio 507 and Panasonic 50'' plasma.
All the sets looked great with High Def feeds. There was a hint of motion blur on the Sony watching some sports action but that was being picky with my eyes. However when the feed was switched to standard definition all bets were off as far the sony was concerned for me. The picture was blocky, colours looked unnatural and motion blur was noticeable on any fast action/movement.
I went for the Pio over the Panasonic because for me the PQ was slightly better on SD, I had read/heard of quality issues with Pany sets (purple snakes etc) and to be honest the Pio just looked better from an asthetic point of view and had a higher quality look and feel.
If you are planning on just watching HD/ DVD or want to use your panel as a comuter monitorgames monitor at lot then think about the Sony. If your normal viweing is majority 'normal' TV and especially if you watch a lot of sport forget LCD would be my advice.
Not seen a 508XD yet but I'm delighted with my 507 and all reports are the 508 is a big step forward. Clearly for that kind of cash (circa £2.5K) you want to go and see one yourself and make your own mind up.
SONY 46X2000 is a pile of junk - edge enhancement bug, poor build quality, poor colour reproduction, poor scaling, poor contrasting and excessive motion blur. Not even in the same league as the Pioneer (or Fujitsu) plasma displays.