The biggest immediate threat to Kindle's long-term viability as a dedicated e-reader is just that -- it's a dedicated e-reader. But why would someone want a device that can only, well, e-read, especially when e-reading applications can turn any old smartphone into an e-book? Sure, the Kindle offers a more comfortable experience -- its screen, compared to the LCDs of most smartphones, is certainly more agreeable. But as smartphone displays become more sophisticated, the Kindle's visual "wow" factor will decline.
Among the most popular e-reading applications is Stanza, the iPhone e-reader developed by Texas company Lexcycle, which claimed 1.3 million Stanza users worldwide as of the beginning of 2009. Stanza also is versatile. It supports a wide range of e-book formats, including Kindle, Mobipocket, Adobe, Microsoft LIT, Palm doc, HTML, PDF, Microsoft Word, Rich Text and EPUB, the open eBook standard that Kindle does not yet support.
Kindle Threat: Nonexistent. Amazon apparently likes Stanza, too, and it bought Lexcycle in April.