Not shilling: I recommend signing up to the weekly newsletter. I've picked up around 9 very interesting books from it. The best recommendation I got from it (subjectively) was Zen and the Art of Motorcycle Maintenance.

I really enjoy the service. Mostly go through all the top books and see if anything calls out to me, and so far the site has done really well at keeping the informal contract of "I give you my email, you don't spam me".

I am aware of this website. Initially, I thought to do the same, extract all links from comments and then figure out which ones are "book-related". However, after browsing several threads I noticed that lots of book recommendations are in plain text.

Ha, that's hilarious because I created one that searches all Reddit comments for products from Amazon[0]. And I'd always been thinking of moving toward searching for all proper nouns, but obviously that's more difficult on this front. So if anyone has suggestions about whether or not to expand and in a certain way, let me know!

[0] http://www.productmentions.com/

This concept I believe represents a good enough sample size to provide a good overview of "most commonly linked-to items." If 100 people link to the same product across many domains, chances are that most of those will be Amazon links. You don't get all of the links, but you get most of them.

The exception will be items from sellers of products not available on Amazon. And there may be some communities in Reddit that are more loyal to another e-commerce platform or site you would miss (crafters to Etsy, antique collectors to eBay, etc.)