A (not so) little Python script I've written. ab.py uses PyObjC to take your Mac OS X Address Book and output FOAF markup, which you can then publish.

ab is still being hacked on, but it works.

Have a look, read the readme.

Now updated to version 0.83 to fix a Unicode bug. Minor enhancements, and it now works properly with Tiger. Grab it compressed, or get the files above.

2004-10-20: I just found that Olivier Gutknecht has done pretty much exactly the same thing — an AB–FOAF converter in Python — though his works with RDFlib. Have a look if this one doesn't do what you want.