I got the UT50 early this year with a Sony BDP-S590. Both are connected using ethernet and connected to each other thru HDMI.
The other day when I decided to take an interest in streaming (setting out on a mission to watch Star Trek: TNG in HD), I ended up deciding to get Prime since they have S1 & 2 available to stream. What I ended up doing was testing between my Viera, my S590, and various streaming services after I couldn't help but feel the HD was really lacking when watching thru the Amazon Instant app on the Viera.
My ultimate conclusion was that there is actually a quality difference between the Viera Amazon Instant app, and the S590 Amazon Instant app. If you have Prime, you can check this out yourself, and I'd be interested to hear if others see the difference. Furthermore, I realized I really don't like Amazon's HD quality.
Vudu had the top HD quality with their HDX streaming. It looked as good as blu-ray to me. If I'm to rent from now on, it'll be on Vudu.
You can play the first 2 min. of a movie on Vudu, and comparing between apps and devices, it seems apps on the Viera always gave a slightly noisier, pixelated image quality. Also, between Vudu and Amazon Instant--regardless of device--not only were action, details, and dark scenes noisier on Amazon Instant, but there was a framerate performance difference.
If you have Prime, you can watch the beginning of Avengers, then watch the 2 min. preview on Vudu in HDX (requires fast connection). There's a lot of dark and detailed scenes. A scene where you glide over some dark glowing stairs, then following a helicopter over a cliff to a compound in the distance with many tiny cars and windows, followed by lots of movement of people. The stair scene in particular is where you can see the framerate difference. On Amazon Instant, the lights thru the stairs sort of lag and drag. On Vudu, you smoothly glide up the stairs. The difference is distinct. You can see the noise and pixels in plenty of these first scenes.
Another comparison is using Star Trek: TNG to compare Amazon Instant between the Viera and S590. The title sequence can be used. There's lots of details in all the windows, seams, and glowing engines, as well as the text, even. On my Viera, I can see pixels around the edges of the text, noise in the glowing engine, softness to all the details. It's like a high-quality SD. When streaming the exact same thing on the S590, everything is more crisp. There's still noise, but it's just the quality of Amazon's video, which after some investigating, I think I read on their site that you only get 720p unless you have a Tivo that allows you to download the videos to it.
This then gets frustrating when I've also seemed to stumble upon a streaming difference between the Amazon Instant apps in terms of connection speed. I get very spotty speeds on the S590. At first it was more often than not picking up a high speed and giving me the HD quality, but more and more, it will keep connecting between 1-2 Mbps(?). After getting fed up, I tried running the Vudu app to see if it was my ISP. Nope, it easily loaded up the HDX like usual. Then I switched to the Viera Amazon Instant app and it consistently tests my speed and gives me HD. When I return to the S590, I keep getting slow speeds. It seems there is a deficiency in the way the app handles initiating connections. It's even tedious in loading the menus compared to the overly-simple Viera app.
As for Hulu, it seems they stream at different rates depending on the program you select. I didn't pay that much attention to it because I really have no interest in spending money on it. I also didn't get a chance to test Netflix as I just recently cancelled with them.