This information seems to be elsewhere, but in separate parts and threads that run off in tangents and discuss multiple issues.

For others finding this, this solution worked (and was required) for me to BOTH use the shared clipboard (bi-directional) and view full-screened goodness in my Fedora instance, from my Windows 7 host.

The important step was not just to ‘Insert Guest Additions CD Image’ from the Devices menu in the host container, but also to go ahead into the Fedora (guest) instance and run (as sudo):

/var/run/media/(myuser)/VBOXADDITIONS(etc.)/VBoxLinuxAdditions.run
And then power off/restart the image.