Have you tried to send PDF files for conversion via email? Does it work?
Also the text on the Amazon help page implies that there is a free way to convert files by sending them to firstname.lastname@example.org
. ("If you would like to avoid the 10 cent charge"). Have you tried that?
Finally, can it handle PRCs loaded on an SD card well? I have a bunch of pdf e-books that I plan on converting to PRCs and being able to read those is the main reason I want to buy a Kindle.