Michael Tyson, a Computer Science PhD student, living in Melbourne, Australia, has created a service (Speak to iTunes Audiobook Service) running on Mac OS X that converts any text to an iTunes compatible audio file. Select some text, invoke the service, and his tool converts the text into a spoken file using the Mac OS X text to speech tool. The file is placed in the Audiobooks section of your iTunes collection.
I installed the service and converted a few articles. I found the result to be pretty good. Not the same as having had it read by a person, but useful none the less.