As I've learned from working on Platypus, programming font operations is one of the most complex and convoluted areas of software development you're likely to run into...ever. It's like driving to the river madness and drinking deeply, then walking around the desert naked for 40 days, all the while reassuring yourself that you must be making progress because you're still coding. It's awful.
The reasons are complex and numerous. First among these is that file formats are capricious things. Microsoft and Adobe have both published numerous font formats--some in response to market needs, others for competitive reasons, still others because of internal pressures. The second problem is that these formats are designed for use by font experts, not by developers. They often include cryptic parameters, tables within tables, and absolutely nothing that is clear or obvious save the copyright notice.
Third is the matter of encoding. There are numerous encodings of font characters. These too seem driven by reasons largely outside of need and formulated with no particular eye to future requirements. Try to figure out encodings for CJK fonts (Chinese, Japanese, Korean character sets), and you'll feel like walking around with your hair on fire. Even in simple encodings, difficulties arise. For example, Apple and Windows use different encodings in the basic character sets, which is why apostrophes in Mac-generated documents show up on some PCs as the euro symbol. Unicode? Foggettabout it. No font today implements close to all the characters. And those that come even halfway (of which none are free that I'm aware), they are huge multimegabyte propositions. In sum, fonts are a topic shot through and through with problems and treacherous details.
Until now, there has been no central reference that developers could turn to for help. Each new font (PostScript, TrueType, OpenType, etc.) required starting anew and learning the peculiarities from scratch . But a new 1000-page book by Yannis Haralambous, entitled Fonts & Encodings (from O'Reilly) has just appeared and it's the first real tie-line to sanity in the jungle of glyphs. It explains fonts, formats, and encodings in tremendous detail; along with elaborate discussions of tools. It is the defining book for technical users of fonts.
Before I discuss two limitations, I want to reiterate that this is a great book and nothing I say should override this view. However, it's not a developer-oriented book. Except for some SVG XML and some TeX, there is little source code. So, information on how to access font data and use it to lay out documents programmatically or just to print text is still left as a challenge to the reader (though the book gets you most of the way there). The book also discussed MetaFont in too much detail, in my view, because this format, which is now little used, is extensively described by its inventor, Donald Knuth. I'd have preferred more coverage of bitmap fonts, say, then re-presenting this info. But these two items aside, this is the book to get if you ever have to do anything with fonts. It'll give you hope; real hope.