Stop remembering numbers meant for a machine, and use DNS. It will make your life so much easier. I spend ~$15/yr for my personal DNS name & hosting, and I never want to memorize an IPv4 or v6 address ever again.
> I have no idea what is using IPv6 and what's using IPv4 right now.
Any "end" machine (laptop, tablet, phone, server) is going to be dual stack, supporting both IPv4 and IPv6. If it is able to auto-configure an address, then it will use those. Otherwise, it won't. If a domain is IPv4-only, it'll use the IPv4 address. All of this is automatic.
The big issue, for home consumers, is that a lot of ISPs are dragging their feet. They don't need anything from the customers — they just need to get it deployed & turned on. Generally, typing "what is my IP address?" into Google will tell you if you have working IPv6; it will display an IPv6 address if you do.
In the cloud… some cloud vendors have been dragging their feet about rolling support out. You need to do some things, like associate an AAAA record to your domain (s.t. it resolves to an IPv6 address), and make sure things like logging can handle the new addresses, or if you implement IP blocking, that you can block those addresses/networks. If you're writing network code, you need to check that you're not assumptions about the socket type. You can also do things like HTTP proxy from an IPv6 connection to an IPv4 VLAN, e.g., I think w/ an ELB. That is,
client <-- HTTP/IPv6 --> ELB <-- HTTP/IPv4 --> backend server
which allows a partial upgrade. None of it is terribly hard, but typical project management puts upgrading to future tech in the perpetual backlog.