It seems you are not alone. Here's a new BZ filed just last night:

  https://bugzilla.redhat.com/show_bug.cgi?id=1064516

It's unclear whether the reporter ran wireshark to turn on promiscuous mode on the host's macvtap interface, the host's physical device, or the guest's interface to make everything work, but you might try those (you could just run tcpdump instead of wireshark - same effect).

In the meantime, I notice that the reporter of that BZ is using qemu-1.6.1-3, while I'm running 1.7.0-4 (which is from the fedora-virt-preview repo). You might want to try enabling fedora-virt-preview in your yum setup, updating, then see if the problem is solved. Otherwise, I guess follow the BZ for progress reports.

  http://fedorapeople.org/groups/virt/virt-preview/fedora-virt-preview.repo