To workaround the issues some of you have encountered when switching fonts on FW 3.x, you'll find here a bunch of font sets packaged as an update file.
To use these, just upload the file corresponding to your Kindle model to the root of your Kindle, and "Update Your Kindle", just like a hack

. You shouldn't need to restart your Kindle at all after that

.
(Of course, for these to do something, you'll have to have the Fonts Hack installed!)
Now, if you want to package your own fonts like this, it's gonna be a bit more cumbersome than usual. You'll be needing a Python 2.x environment, and OpenSSL. If you're on OS X/Linux, you shouldn't have to do anything, that should already be part of your system. On Windows, you'll have to install both.
Python:
http://www.python.org/download
OpenSSL:
http://www.slproweb.com/products/Win32OpenSSL.html (The Light installer should be enough)
Download the kindle-fontpackager-1.0.N.zip file attached here, and unpack it somewhere easy to find. For the purpose of this post, I'll assume it's unpacked in ~/Kindle on OS X/Linux, and C:\Kindle on Windows.
Also take note of where the fonts you want to use are located (And, as always, they'll have to follow the usual
naming scheme). I'll assume they're in ~/Kindle/Fonts (C:\Kindle\Fonts on Windows).
Open your favorite Terminal emulator (cmd by default on Windows), and do:
OS X & Linux
Code:
cd ~/Kindle/src
python ./build-update.py ~/Kindle/Fonts
Windows
Code:
cd C:\Kindle\src
build-update.py C:\Kindle\Fonts
If you're not missing any font files, you'll end up with the update .bin file you need in ~/Kindle (C:\Kindle on Windows)

.