I picked up my 46" Z4100 today. I really wanted to get a chance to see it in person before buying, especially with all the talk of sparkles. Got offered a good deal and jumped on it. So far I'm really happy with it.
First, yes, I see sparkles too. But I have to be zipping through my PS3 XBR menu, and I have to be looking for them. Otherwise I haven't seen anything. Even when I do, it's so minimal it would never bother me.
Second, I have a HDR-SR12 Sony HD video camera with xv color. I don't know if it's the compression ratio or the xv color but the videos from my camera on this tv are absolutely stunning. IMHO, they looked noticably better than 1080i video from Cablevision and even the blu-ray video playing through my PS3. All 3 were connected via HDMI cables.
The video off my HD camera was so sharp and the colors were so alive.
I'm going to do some videos with xv color on and off and try and compare.
I'd highly recommend both to anyone considering either of these fine toys...