Some clever people posed a interesting issue regarding GPL, the copyleft license drafted by Free Software Foundation (FSF). Some fonts are GPL'd. What if I used such fonts in my document, should I redistribute my piece of document in GPL as well? FSF response to this issue by adding "font exception" in their GPL. I think this issue is not as complicated as its discussion in Slashdot and adding font exception to GPL is ridiculous. Are the folks in FSF also misread their licenses?
As per my understanding to GNU family of copyleft licenses, one can use (execute, read or even modify) the material licensed in GNU family of licenses (ie. Software licensed thro GPL, document licensed thro GFDL) virtually no limit. GNU family of licenses only govern the way you redistribute the derived works. The document you produce by GPL'd software (eg. an artwork produced by GIMP, a document produced by OO.o) can be license in any way you like and not limited to GPL. The same is true for GFDL. If you followed a GFDL'd manual and created a robot, you don't need to license your robot as GFDL.
However, if you produce another piece of material by modifying / incorporating the material licensed by GPL/GFDL, you have to license your material by the same license. For example, if you incooperate the content of a GFDL'd robot building manual into your Cruise Missile building manual, you have to license your Cruise Missile building manual to GFDL.
If you type a document in GPL'd fonts, I found no reason for you to license your document in GPL. It is because a document you type cannot be consider a derived works of fonts. It is a derived works of your brain. Moreover, the document itself is a brunch of data, not program or source code under the term of GPL. Even you produce a 7 dollars newspaper with GPL'd fonts, it is ridiculous to think that the source code of the newspaper (eg. the LaTex files, .doc files) should also be licensed thro GPL.
However, if you modify the typeface of GPL'd fonts (say, by modifying the "source code" of fonts, but technically not possible) and incorporated in your font collection CD for sales, you have to give out the source code of your modified GPL'd font in GPL terms.
The viral nature of GPL/GFDL is not that monstrous.