And to expand a bit on the FreeType override feature:
First of all, FreeType is the name of the library used to render the fonts on the Kindle. Meaning, it's the most important part (software-wise) of the font rendering chain, and it can have a *huge* impact on how your fonts will look.
As I said a couple of times already, the settings used for FT on the default firmware changed drastically in FW 3.x, and while it may be a bit crisper than before, it depends hugely on the quality of the fonts. (In short: it can look very nice, but it's less compatible, it doesn't handle crappy fonts very well).
Now, with this, you can choose if you want to use FT's autohinter (like FW 2.x), or the fonts native hinting (like FW 3.x). In both cases, the FT lib used is way, way more recent (especially in the FW 2.x case, which is using a prehistoric version of FT that must be patched all to hell), so, even if you choose the same type of rendering that the default on your FW, it *will* look different (at least slightly).
There is also another choice, the 'light' autohinter. It tries to preserve the glyph's shape better than the classic autohinter, at the expense of a slightly fuzzier rendering. It's a bit like OS X's font rendering.
But, it will garble the glyphs shown in the Symbols & Note popups, and the browser address bar. (Which work fine with the other two settings). I don't think there's anything we can do about it, it probably stems from the fact that, for some (stupid?) reason, the Kindle renders fonts without hinting nor antialiasing in these popups...
Take into account that I'd consider this a fair bit more intrusive than usual, that's why it's not enabled by default. That also means it should be considered experimental, as it may be on the crashy end of things (crashy as in 'make the framework crash & restart', not lockup). I've tested this on a K2i & a K3 without any apparent issues in the Menus/Reader/Topaz reader/Apps/Browser.
And finally, to enable this (it's already specified in more detail in the first post, but here we go

):
To use FT's autohinter: Drop a blank "autohint" file in the linkfonts folder.
To make FT use native hinting: Drop a blank "bci" file in the linkfonts folder.
To use FT's light autohinter: Drop a blank "light" file in the linkfonts folder.
If both files are present, autohint will be used.
You will *have* to do a *full* Restart for this to be taken into account.
On the good news front: It very well *may* fix the 'blank fonts' issue some of you are having on FW 3.x. So I'd gladly welcome feedback on that front, given that I still can't reproduce this on my Kindle

.