The headline says it already:
Peter Robinson has update the Tapioca packages for Fedora Core 5, and they are working now again (at least for me). The problem was a farsight error (as far as I know) which is now fixed.
The quality haven’t changed so far, btw., my call partner on a Google talk client reported reported the quality as not as good as skype and a way noisy. Therefore it can be used for some minutes, but not for a call over an hour or something.
On my side the quality was nice enough to call for a long time: the sound was a little bit metallic, but that was ok.
I hope these problems will be fixed when the time goes on. Besides, I spoke already with Peter about future updates of the packages, and he agreed to try to test new packages before they are uploaded to the repository.