I have disabled ipv6 permanently since F14, and no problem. Just add "install ipv6 /bin/true to /etc/modprobe.d/dist.conf"(old variant) or "blacklist ipv6" to /etc/modprobe.d/blacklist.conf and "net.ipv6.conf.all.disable_ipv6 = 1" to /etc/sysctl.conf. There is nothing you cant control in your Fedora setup.