Loopback in Yosemite not working
This might possibly be not the best long-term solution - I can't fully test as I don't actually have active IPv6 from my ISP yet, only on my local network.

I simply set my hosts file to

127.0.0.1   localhost
255.255.255.255 broadcasthost
::1             127.0.0.1 
fe80::1%lo0     127.0.0.1


which has so far given no noticeable issues.