Initially, Amazon's Personal Document Service would push converted files to your Kindle for a flat $US0.10 each. Well, changes are afoot: Amazon has announced expanded format support, but a higher fee of $US0.15—at least.
The way things used to work, a single dime would cover a Whispernet delivery of anything from a simple JPEG photo to a 120-page manuscript of your Xena: Warrior Princess fanfic novella. Starting May 4th, Amazon will introduce a progressive payment scale, based on the size of the transferred document. It's pretty simple: $US0.15 for every megabyte transferred over Whispernet, rounded to the next whole megabyte. In effect, this means that the minimum transfer charge is $US0.15, and that larger documents—but still of a size that people regularly transfer to their Kindles—could cost upwards of 50 cents. In other words, you'll be paying a minimum of 50% more than you used to.
It's not all bad news, as the conversion service now accepts DOCX and RTF files, adding to an already ample list of supported formats. And the conversion service on its own is staying free, so you can still have your documents converted to .mobi and returned to you via email, after which you can just load them to your Kindle via USB, like everyone already does anyway. [Geardiary via Engadget]