There has been some recent confusion about font licensing. Since I wrote the font exception, let me tell you a bit about where we are, and how we got there, and what this all means to you.
First, in the US, the copyright status of fonts is somewhat confused. A font face -- that is, the look of a font, is not copyrightable (see Eltra Corp. v. Ringer, 579 F.2d 294 (4th Cir. 1978)). But font "programs" (truetype fonts, for example) are. Another ruling has extended the definition of "programs" to include certain outline data. Why this outline data is not equivalent to a font face, nobody knows. Helpfully, the copyright office has also issued contradictory statements on this. I don't know how font copyright works in other countries.
What this means is that no font is going to affect the
distributability of a printed document in the US. Further, merely
referencing the font (as in the CSS
font-face: caslon;) does not create a
derivative work of that font. So why did we worry about font licensing
The situation we were considering was one where a font was embedded in a document (rather than merely referenced). Embedding allows a document to be viewed as the author intended it even on machines that don't have that font installed. So, the document (a copyrighted work) would be derived from the font program (another work). The text of the document, of course, would be unrestricted when distributed without the font.
This isn't an artifact of the GPL; it's just the way fonts work. Proprietary fonts often explicitly forbid embedding. So, if you want to send your document off to a printing service, the printing service needs to buy another copy of the font.
I was unhappy with even this amount of influence for fonts, because (a) it's rarely what font authors intend and (b) it's possible that some applications do embedding behind the user's back. The situation seemed to me to be similar to the case of the runtime libraries which GCC automatically includes in its output (and which are licensed to permit inclusion in proprietary software). So, I wrote the font exception you see on our web site.
The reason the exception is so limited is that we're worried about someone extracting a font from a document, and redistributing it. Extraction is, in my view, the major issue that a font license must confront. Because I haven't been able to come up with a license which correctly handles embedding and extraction in all cases, I've restricted this exception to unaltered fonts. This means that someone can't use embedding as a way to distribute a modified version of a font under restrictive terms. If you have suggestions for how to write a license which better handles extraction, please let us know. We haven't had time to give this as much thought as we've given some of the other issues involved in free licensing. We're especially interested in hearing from font creators at firstname.lastname@example.org.