I installed today's F19 on the 6 GB Core Duo 6550 machine today and ran yum update.
This time I downloaded the rpmfusion files and installed them with rpm. Vlc and ffmpeg installed without problems. VirtualBox refused to install.
I was able to get the virtual machine manager to start installing SCO Unix. Installation slowed down to "slower than a mole in granite". It has been stuck at 80% installed for the last half hour or so, using 100% of one core. There is no unusual HD activity.
When not broken, VirtualBox loads SCO quickly.