I've been looking at Bookswim for at least a year now, and finally decided I'd give it a try. Of course it's most often compared to Netflix, and that's a very apt comparison, though Netflix recommendations and categories are far more advanced than Bookswim's.
Bookswim does have an amazingly deep catalog though, and the turn around on getting my books was fast. I have yet to return any, so I'll have to update when I do that. I ordered my books on Saturday, received an email on Monday and received the books on Friday, which isn't bad considering it's shipped USPS Media mail.
I love my local library, and I like visiting bookstores. But Jackson, the closest city with a bookstore, has very little to offer. My local library, and the Jackson library, are very helpful and I use the interlibrary loan program regularly, but there are just some books you're not going to find through ILL, and when you do, you may get them at a point when it's difficult to read them and get them back in on time. Bookswim seems like a good solution for book fiends.