As a returning Kindle user after an ~7 year gap, I was pleasantly surprised to learn how easy it is now to add custom fonts to the Kindle. No jailbreak, no hacks, just easy peasy.
I didn't realize you could do this so easily until I stumbled across it in the new PW User's Guide, 4th ed., Ch 7. It boils down to: connect Kindle to PC, browse to the
/fonts folder, and copy custom font files in there. Basic directions are in the Readme.txt file in the
/fonts folder, if needed.
Geez that is great news, I'm a happier PW4 owner than I was yesterday.

Hope that other new-ish Kindle owners are aware of this. I usually don't read the manuals, so I was lucky I ran across that.