Deltaisos are available at
http://thepiratebay.org/user/andre14965/
for Fedora 12 -> Fedora 13 Alpha DVD images (i386 and x86_64).
i386:
Fraction of full ISO size: 38.6%
applydeltaiso's approximate running time: 41 minutes
x86_64:
Fraction of full ISO size: 38.5%
applydeltaiso's approximate running time: 44 minutes
Instructions are at
https://fedoraproject.org/wiki/Delta_ISOs