Eep!
@Anarel: I cannot possibly make it clearer than in the first post/wiki. Whatever I might answer you here is already written in greater detail in the first post and the WiKi

. Very succintly: The hack uses 12 font files (+2 for CJK/I18N). You switch these 12 files, and you restart your Kindle.
@gargoyle67: That looks like a full Serif to me, so no, not the default font. I'd say Droid Serif, which is the font installed by default with the fonts hack.
@gargoyle67 (bis): No, your folder looks fine. Although the custom fonts there looks like Fontin, which is *not* the font used in your picture...
@Tvangeste: Great

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@daffy4u: Because that's before the font hack first ran. It copies over all of the default fonts that you see on the other screens.