Per the link below, it looks like Amazon Unbox has finally discovered HD is where it is and appears to be launching a product, however they appear to be Shafting Tivo as this service is only earmarked for PCs.... I recognize that is only a survey, but if they were concerned or interested in the Tivo market we would have seen one by now!!
http://gizmodo.com/362637/amazon-unbox-hd-rentals-coming-soon
Anyways, this is why time and time again, I have relentlessly beat on Amazon Unbox with their lack of quality content (Widescreen, HD & Dolby 5.1) they are making available to Tivo users - specifically those users with Widescreen TV's and more importantly Tivo HD units with Dolby. Anyways, peruse the link and pass along your cursory thoughts.
Edit: That link I provided is only for Question 19 of the survey, So it might be more relevant to Tivo, however I was not offered the survey (Good thing for AU).... Anyways, if somebody else has the survey link or list of survey questions they can provide, that would be great as it might help to determine AU's interest in providing a more robust offering for Tivo users.