I tried out for the first time yesterday Amazon's Unbox Video-on-Demand service and its integration with TiVo.
The link process between my Amazon and TiVo accounts was quick and painless, and the process of ordering a movie rental couldn't be more straightforward.
Unfortunately, even with a fast 802.11g wireless network, the download of the movie ("Casino Royale") onto my TiVo Series 2 took almost as long as the movie itself runs. More importantly, all motion (whether it was a car chase or simply the movement of people across a room) was distractingly blurry throughout. It kind of felt like you were watching the movie in a perpetual, drug-induced haze.
Maybe Amazon Unbox through TiVo works well for movies in which there isn't much action, but for action films, I think you'll start to get dizzy just watching them.
I think this is a great first try, and I look forward to future improvements.