I can't, and won't try to, speak to the issues anyone might be having with JAWS 17 or 18.
What I can speak to, though, is that very often, for any software, if you are using the "install over" method of installation or upgrade method a tiny problem will be introduced that shouldn't be (and not through the fault of the user - you don't control the installation/upgrade software). These can be carried along and unintentionally built upon until they bring things to a grinding halt.
Tim said, "I completely uninstalled every piece of FS software, other than Open Book, and did a new install of JAWS 16 from the installation CD." I'm not saying that I know the answer to the question I'm about to pose, "What would have happened had you done the same with JAWS 17 or JAWS 18?"
The "uninstall it all" reboot, and reinstall from scratch technique sometimes works to resolve what seem to be insoluble problems. If you want to be really thorough after the initial uninstall and reboot, you might want to run a utility such as Revo Uninstaller to be sure that there are no vestigial traces of the prior installations anywhere. Some uninstallers are much better than others about cleaning up after themselves.
I've solved a number of problems with various JAWS installations for releases well before either 17 or 18 by taking this approach. It may solve nothing for all I know, but it's definitely worth a try to see whether it does.
~ William James