I finally signed up for a free trial this evening an tried a few films. I tried ones that are available on blu-ray so I know the source is available in HD. What I got was clean in terms of framerate, but it is "foggy" as it is enlarged quite a bit. The "source" is a small screen and when letterbox is chosen, it gets pretty blurry. I've got a 6Mbit connection and get 4 bars and no stuttering.
I found a blog that described the delivery process and it isn't exactly impressive. Hopefully they'll improve on it with time. Granted, it seems better than SD television, but still not what I had hoped.