Reminder yet again that Amazon and Kindle are important parts of the mobile, cloud, content and application universe... these are the registered Kindle devices to my family: it's a combination of devices, platforms, formats, etc. More and more I am using Kindle like Evernote (one of my daily, most-used applications): I forward important documents to my personal Kindle emails. It's great. And for some use cases, its the equivalent of Evernote or iCloud.
And like Evernote - the content is accessible anywhere, nearly instantly. I love the email component of it and think that personalized emails as a content direction / entry mechanism are underutilized - Evernote and Tripit are examples of products that (for me) are most useful through email.