The same things I use IPv4 for. Just because there is a plethora of IPs available does not mean you have to use all of them. Providers assigning a ton of them by default is just a "feel-good" state of thought after the IPv4 depletion depression.
Hey guys, I just wanted to throw this out there for some to think about:
I tend to use ipv6 for back-ups and for large traffic items. Why you may ask? Well, most of the time (NATIVE) ipv6 is a separate infrastructure, as a lot of people are not very familiar with ipv6, usually the routes are not as saturated. When doing back-ups and transfer on server with (NATIVE) ipv6, you may find you actually get better speeds and latentcy than using ipv4 on the same server. For example, one of my server in Germany that I have with native ipv6 I actually can get full 11Mb/sec (100mbit) transfer to my backup server in the US almost anytime, while over ipv4 it will get stuck around 5Mb/sec because of the route saturation.
While it may not be main stream yet, this may also be another reason to take advantage of it now, while people are not over saturating it. Also something to keep in mind, while some may have really good routes for ipv6 in place with a decent commit, some may not, so what I am saying may not hold true in all situations.