The Use of Amazon Affiliate Links
Amazon Affiliate links are useful things. There's even a WordPress widget that let's you add them easily to any post, which is very convenient. Many authors have taken to using them to add their books to the sidebar of their site, or when they're doing reviews of someone else's book. I have to warn you - this may be a very bad idea. Please allow me to introduce you to a rather interesting little plugin called Adblock.
Now You See it...
Adblockers are the most popular plugins for Firefox and Chrome, representing over half of all net traffic. What they do is very simple, at heart: they have a blacklist of different advertising programs, which is being updated all the time, that cuts advertising sections from every webpage a user visits. There's adblockers for every major browser - yes, even Internet Explorer - but the Firefox and Chrome plugins are the most well known.
They turn this:
...Now You Don't.
They treat your Amazon listing in exactly the same way, because the blacklist includes anything in Amazon's Affiliate program. Poof, no more books showing up on your website.
If you're actually using it to get affiliate revenue, then great, you can leave them in and take your chances with adblockers. But this is one hell of an issue if you're just using the links for an easy way to display your books on your website. This means that there's some unknown number of visitors who never see your books and never get a chance to click through and buy a copy - and you'll never know if that's just one or two, or if it's a significant percentage of them. It's also likely that you've never been told about it if it is happening, because the cut is damn near invisible. It's usually impossible to tell where the advertising should have been, so a new visitor who doesn't know you will probably assume you only have your books listed elsewhere on the site, like on a main book page.
This was brought to my attention specifically because I asked one of my authors why they didn't have an easily accessible book list in their sidebar. Turns out they did - I just never saw it.
So what about book reviews?
Plenty of sites do book reviews and run on their affiliate revenue. Again, it's all about what you're using the links for. If it's worth the affiliate cash, then go for it and be happy. But if you're using them for convenience, then you might want to figure out another way of displaying your books so that everyone who comes to your site can see them.
This isn't a make-or-break thing. It's just something you need to be aware of. The best thing to do is get Chrome or Firefox, if you don't have one of them already, and install an adblocker plugin. Then check your site. If your book list has vanished into the ether, then you've got a problem - not a big one, not a critical one, but one that could be costing you sales.