Here's a useful python tool for reducing the size of MOBI files created using Amazon's Publishing kindlegen tool.
Basically, kindlegen includes the original .html, .epub, ... file inside
it's created .mobi file. You really don't need this, but it's
speculated the reasoning is for future compatibility. (Read the
comments at the top of the file for more information.)
If you publish, then you likely want to strip this extra data so you use less bandwidth on the remote host, saving you money.
The author made a post to MobileRead
posting his Python script. Unfortunately, the script was likely
created with a Windows editor placing ^M at the end of each line.
I've edited this out for Linux users and am placing this script on my
site for easier access. (Especially since Forums may disappear