Do you mean you want to add your own reviews or the ones provided on the Amazon website? If you mean the latter I use a script that you can get from affiliate-developer.com which provides that function (as can be seen from my site igdb.co.uk/guitarshop/ - make sure you type the '/'). If you mean add your own reviews, no idea...
I was thinking a feature that added the reviews to your own site so that you could create some unique and fresh content for youe own site.
Adding product reviews is pretty easy to do with most Amazon stores if you know how to work with code and a database. Just use the Amazon ASIN as the key for the review. The problem is the writing of reviews for a large number of products and a product mix that's always changing. The newest version of Ghostscripter has a built-in feature for users to add reviews, but I don't know of anyone who has received a response from the Ghostscripter guys for at least six months. They may have gone belly-up or have abandoned the script.
Would it be against the terms of service to create a script that add the reviews to your own website?
I don't see how that would be a violation. You don't have to use Amazon reviews on your product pages. I do have a site where I cherry-picked the best Web development books and wrote my own reviews for those products.
I think there's already a mention in one of the posts that GhostScripter script has an option to turn reviews on..
That script doesn't add the reviews to your own site though. I think it would be great to build a script that stores the reviews only on your own website. This would help to avoid the duplicate content penalty.