Well, if you loved the idea as much as I did, but didn't think you'd be using it enough to justify coughing up some dough for it, you're in luck. Over at Mac OS X Hints, user miketyson has created a script that will add a service to your Mac's Services menu. The new service, which is appropriately called Speak to iTunes Audiobook, allows you to select a body of text and automatically have it converted into an audiobook, then have it imported straight into iTunes.
In testing the script works as advertised. My only quibble is that the clipped audiobooks don't get any sort of meaningful name given to them. They are simply named Speech 1, Speech 2, etc. If the script was smart enough to look at the title of the document the text was being clipped from and generate a title from that, this would be a killer utility. But that's really only a minor complaint considering the heavy lifting this little script actually accomplishes. And heck, if you find yourself using it, you might consider going back and giving GhostReader a second look.