In fact, I believe that library-sector developers have asked Amazon and 
been told that their use is allowed. But definitely, there's no 
guarantee this will always continue be true. The terms of use don't seem 
to have substantially changed to me, but they could always start 
enforcing them more strictly -- for new accounts created to use the 
Product Advertising API, it looks like there actually will be a manual 
review step where Amazon staff approves you or doesn't, which never 
existed before.

So, while I'm still using it, I'm also keeping in mind what backup plans 
I have if they ever ask me to stop.

Here are the things I use Amazon API for, with alternates:

1) To take an ISBN, and look up more complete metadata for it.  
    A) Google Books Data API (free for everyone; yes, there is a GBS API 
which is explicitly authorized for non-javascript access. GBS API will 
also allow you to find OCLCnums and LCCNs that correspond to an ISBN, 
when GBS has that data, which it often does thanks to the OCLC 
    B) WorldCat API (OCLC members)
    C) Books In Print API, although BiP seems to be making up their mind 
about whether they'll throw this in for free with an existing BiP online 
subscription, or charge extra for it.
    D) OpenLibrary? (Is this true?)

2) Cover images. Alternatives:
    A) CoverThing
    B) Google Books
    C) OpenLibrary

3) To find an ASIN, in order to make a link to the Amazon page.  
Ironically, this is actually what the API is _for_, and what Amazon 
would actually WANT you to do, but it's the thing that's least 
replaceable.  If you have the ISBN, and if you assume the ASIN is the 
same as the ISBN, you don't need an API.  This is often true, but not 
guaranteed to be true, and I think will become less true when the new 
ISBN-13 namespace starts to be used.   In my case, I use the ASIN to 
identify if Amazon has a search-inside and/or limited-excerpts 
available, but the API actually doesn't support that, I've been 
screen-scraping all along for that, once I have the ASIN.

Tim Spalding wrote:
> They're also tightened up the API in various ways, and renamed it the
> " Product Advertising API." Although I know of no case when
> Amazon has shut down a library, it would be hard for any to claim
> their site had "as their principal purpose advertising and marketing
> the Amazon Site and driving sales of products and services on the
> Amazon Site."
> I think it's a terrible mistake for them. Their marginal cost is zero;
> they don't need to do this. Data openness was a key factor in Amazon's
> rise. And that was when thee were no other options. With viable other
> options just emerging—Open Library, Google, at least—now is hardly the
> time to make it less attractive.
> Tim
> On Mon, May 11, 2009 at 9:40 AM, Jonathan Rochkind <[log in to unmask]> wrote:
>> The Amazon products API keeps changing it's name, and has just been changed
>> to Amazon "Product Advertising API" -- it's the one you use to look up books
>> in Amazon and get metadata for them, though.
>> It looks from an email I got from Amazon that ss of August 15th, you'll need
>> to cryptographically sign requests to this API, to have them responded to.
>> It looks like kind of a pain.
>> I think a bunch of people on this list may be using this API. Beware.
>> Instructions for how to cryptographically sign requests the way they want
>> can be found here:
>> Like I said, it's looking like a pain to me. There are lots of details to
>> get right. If you URI-escape not _exactly_ the same way they do, it's not
>> going to work. Etc.
>> Jonathan