As I noted recently ( Fedora 17 and updates-testing ) In the run up to Fedora 17 release, the updates-testing repo has been disabled. If you are wanting to use 'yum distro-sync' to sync your pre-release machine up to stable updates/base repo packages only, there's a few gotchas you might run into:

• First the fftw package decided to reorg how it's subpackages were setup. (IMHO not a great idea right before release). The version in updates-testing is one libs package, but the base version is a bunch more subpackages.
• Next you may run into colord-gtk issues. colord grew a new colord-gtk subpackage (IMHO not a great change right before a release either).

To work around these, try: yum shell remove colord-gtk remove fftw-libs-double fftw-libs-long fftw-libs-quad fftw-libs-single downgrade colord downgrade fftw-libs distro-sync I'll try and update this post with any more of these I find... feedback welcome.