I'm not sure if the OP has picked one of these sets yet, but I was at my local Future Shop yesterday picking up a movie and decided to demo both tv's since I'm also deciding between the two.
I managed to get one of the sales reps to take the Dark Night disc out of the Sony display and put it in the Panasonic first. However, the comparison was a little unfair for the Pioneer as it was on the display floor while the Panasonic was in a dedicated room. On the Panasonic, i changed the input to THX mode and watched the underground scene when Joke was trying to kidnap Harvey Dent. The image looked nice, but I noticed all the dark areas looked a little grey. It honestly didn't seem like a huge improvement over my Panasonic LCD that I bought last year. My roommate stopped by as well and noticed the same thing.
I then popped the movie in the Pioneer that was on display outside and tried the Movie & Optimum mode. I set the BD to the same scene and re-watched it. Honestly, even with all the lighting and reflections on the screen I instantly noticed the image looked better and can easily tell the blacks were darker. I asked my roommate what he thought and he noticed the exact same thing. Now I really wonder how much better this TV would've looked with the same setup as the Panasonic.
After this viewing, I think I've decided that the Pioneer is far superior. I read the CNET review saying the Pansonic was better because of colour accuracy but my eyes don't lie. Also, currently the price premium for the Pioneer is $200CDN more than the Panasonic so the only problem I think I'm going to run into now is which stores will still have it in stock.