In the "getting started" instructions: https://fedoraproject.org/wiki/Getting_started_with_OpenStack_Nova we download Ubuntu images from rackspace and use those for testing. We should really have Fedora images available for this
We now have instructions on building Fedora 15 images with Oz: https://fedoraproject.org/wiki/Getting_started_with_OpenStack_Nova#Building_an_Image_With_Oz
Another option to build an image is appliance-creator (based on livecd-creator but instead of ISO, partitioned disk image is produced). For F16 images, we need to fix blocker bug 744390 - Add support for GRUB2
danpb is publishing images here: http://berrange.fedorapeople.org/images/