Never mind that last bit above--I am now using the modified version of the plugin's PHP file above (post #85 by Hidden Gamma), and I see the modified lines. (I had manually made changes, but missed two lines.) So the regex is fine as is.
Nonetheless, I ran the plugin as a regular PHP file (removed the function syntax), assigned $text manually, and found out that the plugin's PHP file is rewriting the URL correctly, with our associate ID in it. So, the problem does not appear to be with the
functions_amazon_links.php file.
And those with .co.jp and .co.uk should be happy to know that those URLs are rewriting properly as well (the domains show up properly).
So for some reason, the rewritten code is not making it to the posts, either when made as a new thread, a normal reply, or a quick reply.
Someone with access to a web server can test this themselves also. Comment out this line at the top of the file:
PHP Code:
// function amazon_links($text) {
Right below it, use something like this:
PHP Code:
$text = "[url=\"http://www.amazon.co.uk/No-Line-Horizon-U2/dp/B001O0EQ5U/ref=sr_1_1?ie=UTF8&s=music&qid=1243921433&sr=1-1\"]Click Here[/url]";
At the bottom of the file, comment out these two lines:
PHP Code:
// return $text;
// }
...and add this line below it:
Run this file in the browser, and you'll see the output with the correct country's associate ID inserted, and the correct domains in the URL.
So my hiccup has to do with the hook location...? Or the PHP code that calls the plugin? This plugin file works, but changes don't end up in the finished post. Once I solve that, I'm golden.
One added bonus: we have one or two members who "innocently"

post Amazon links to a CD, with their own Associates ID inserted in the URL. This will kill that, and save my staff having to sniff these out.