From what I can tell, Apple have changed how fonts work in iOS 7 and it is no longer a case of changing the glyphs in a few select font files and everything looks different. For example, the Weather app has several different fonts in it, even those that look the same size and font are in fact two different fonts that just look similar and have different names. Some apps won't load unless the default font is used or the custom font is a perfect replacement for the old one.

Anyone tried tackling the font in iOS 7 yet? I have most of the other tweaks sorted and having the stock font replaced is probably the final one. I've managed to replace some of the fonts but some are still proving to be difficult. Cheers.