Just wanted to post my experience:
I went to my local sears last night and they had both the PK750 and PK550 on display!
The two sets were in different isles so I was able to compare both against LCD and plasma displays from samsung, Sony, sharp, Panasonic. Also the remotes were available for all the sets so I was able to adjust the settings from the super bright store shelf level for comparison.
Ok, for both sets, 550 and the 750.... They just looked washed out and dull compared to every other TV around them!

I adjusted, and re adjusted and I could not get them to look vibrant compared to the panny and samsung plasmas and the samsung and sony LCD's! I was really disappointed overall with both sets! I know that they were being run off the store feed over coax, but so was every other TV that I compared these too!
There was an LG LCD (sorry forgot the model) that was next to the 550, and the picture looked great, not dull or washed out!
I know this was a very unscientific test done in a store... but It was really obvious how much less vibrant and detailed the LG's looked compared to the other sets on the shelves. I even looked back from half way across the store and could tell which one the LG was because it looked dull!
I had high hopes for these, and I was seriously considering one... but after seeing them in person Im really re-thinking it!
Anyone else notice this when comparing?