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The Amazon Kindle eBook store is the biggest and most widely used eBook store on the web.
Specs
Pros
Pro Often has lower prices compared to other eBook retailers
Amazon being as large as they are can often undercut the pricing of eBooks. This is not always the case as a lot of eBooks have their prices set by the publisher. this is called agency pricing. But on non-agency eBooks Amazon is often the cheapest store.
Pro Kindle Owners' Lending Library
The Kindle Owners' Lending Library is a feature of Amazon Prime, a service that costs $99 a year that includes such features as free two day shipping on Amazon orders and a membership to their video and music services. The Kindle Owners' Lending Library has more than 600,000 books users can borrow (one at a time) with no time limitation.
Cons
Con All eBooks are in a proprietary format
Unlike other eBook stores, Amazon does not offer .epub's (a free and open eBook standard) for their Kindle devices. What they do offer is a proprietary format that only will work on their own Kindle devices. Sadly this creates user lock in as there is no way to take those digital titles to another reader without stripping the DRM from them (something that may or may not be illegal in certain countries) and converting to a format that does work on said other devices.
Con A lot of books are copy and paste from the web
Large selection, but there is an ever increasing numbers of books that are less than 100 pages, mainly created copying and pasting freely available information from the web. Searching for what you want is becoming difficult, with results showing lots of pointless and poorly written small books.