Send to Kindle is an app developed by Amazon to make sharing documents to all of your Kindle devices a drag and drop affair.
Previously, users would have to connect their Kindles to their computers or send the documents over email to a specific address but that was inelegant and cumbersome. Send to Kindle simplifies the process. All you have to do is drag and drop your files into the Send to Kindle window, select which device(s) you want the documents sent to, and you're done!
During testing, our registered Kindle apps for iPhone and iPad showed up as well as our Kindle ereader. There's also an option in Send to Kindle to send documents over Whispernet, Amazon's 3G syncing and delivery service. Be aware that there are charges for sending data over Whispernet ($0.15/megabyte within the USA).
Our files and documents showed up immediately most of the time. Larger files and PDFs that need to be reformatted to Kindle will take a while longer. Amazon also saves these files to the cloud so you can re-download them later if you deleted it off your device.
Overall, Send to Kindle is a beautifully simple way to get documents and files to your Kindle.