It seems like just the other day that I was testing Amazon's Video on Demand as seen via a Roku Digital Video Player. In fact, it was just the other day. But serendipitously, the digital ink was barely dry on that post when Amazon launched its new High Definition content on Video on Demand, so it was back to the salt mines for me. Laying on the couch testing this stuff is grueling work, let me tell you!
Anyway, I really wasn't sure what to expect. Internetfrog.com says I was getting 7.87 Mbps download during my testing. The Roku player suggests a minimum requirement of 4 Mbps, but doesn't specify if they intend that for standard or high definition playback. The Roku has no internal hard drive so can't rely on any significant buffering. Amazon's site says you need 1.5 Mbps for the best SD experience (though they support speeds as low as 450 Kbps) and 3.5 Mbps for HD (720P). I was prepared for the worst, and hoping for the best.
I'm happy to say, what I got was closer to the best. It took slightly longer for the show to begin, but once it started, it played with almost no problems. At one point, for just a few seconds, there were some digital artifacts, and there's still a tiny bit of banding on large monotone background areas (walls, generally). The latter I only noticed because I was looking for problems and not focusing on the action happening on screen. The artifacts were more intrusive but frankly no worse than those that pop up from time to time on HD cable channels.
Amazon bumps the price of content up by a buck for HD: for TV episodes $2.99 HD vs $1.99 SD, for movies $3.99 HD vs $2.99 SD. Those prices are for buying TV episodes and renting movies for a 24 hour period. At this point you can only rent HD movies, while you can either rent or buy SD movies ($14.99 seems to be the 'standard' cost to buy a recent movie).
While I tested the HD content on a Roku Digital Video Player, you can also access it via a Tivo or any of the other devices supported by Amazon, including via web browser on a reasonably modern PC or Mac.
Final verdict? Thumbs up. The price of movies is comparable to renting a physical disk (without the hassle of leaving home), and the quality is fine for casual movie watching. You'll still want to go Blu-ray for your favorites though, for the full 1080P experience (plus all the bonus features if you're into those). I'm not as convinced that it's worth a 50% increase in price to upgrade from the solid SD experience for TV shows; it would depend on the series. Battlestar Galactica: yes, The Big Bang Theory: probably not (but your mileage may vary).