So, you hacked the Kindle
No. There have actually been a number of other user-generated Kindle updates. igorsk created the toolset which generates Kindle and Kindle 2 updates. Other members of the Kindle community have created Kindlem2 updates which change the Kindle's fonts to support books in non-western language, let you set your own screensavers and a bunch more. These packages already contain everything a technically savvy user would need to install software on the Kindle. What I did was to port an ebook-conversion package to run reasonably efficiently on a 500mhz ARM with 128 megabytes of system memory and to write a small program which watches for new ebooks in a few chosen formats and run those through the conversion tool.
 How does it work?
Savory installs several programs on your Kindle 2. (This program only works with a Kindle 2.) First is a small program which runs all the time on your Kindle and watches for new files in the 'Documents' directory with names ending in '.epub' and '.pdf'. When the system notifies Savory that a document has shown up, it wakes up and runs an open-source file conversion program called Calibre (modified and trimmed down from the standard version).
Savory changes the browser configuration file to allow download of pdf and epub documents. It adds a new "init" script which tries to mount savory-image.ext3 on boot. If that succeeds, it runs bin/savory_daemon from within the image mentioned above. Savory_daemon is a Python script that watches the documents/ directory and invokes the converter based on Calibre when it sees something that looks right. Calibre converts the file to Mobipocket format so that the standard Kindle can read it. (The original files are saved on the device and can be downloaded to your computer later.)
Savory was last updated November 2009. For more information see Jesse Vincent' blog or threads at MobileRead "Savory - a native ebook conversion package for the Kindle 2" and "Savory for Kindle International"