The Early Access program has been open for some time and when I signed up to it I was in the 4th wave. The way that CloudFlare domain registration works is a little different to the usual registra in that you have to have your domain already active on CloudFlare. This is no drawback whatsoever of course because you get the benefit of a (free, unless you want advanced features) CDN and cheap domain registration in one. The way I see it is it's a deal that's almost too good to be true, but it is!
After signing up to the early access program, you will get a bright purple box appear on your Home page that lets you start transfers of your domains to CloudFlare.
The transfer process is fairly simple and if you've ever transferred a domain in the past you will breeze through it. All you need to do is select domains to transfer, enter authorisation codes from your current registra, enter contact details and let CloudFlare do the rest. By default CloudFlare tries to add all of your active domains to the transfer list, you can easily remove any you don't want to transfer however.
But there is a catch. There had to be one right?! Not all domains can be transferred at the moment. The big ones like .com, .net, .org and .info are transferrable right away. Other TLDs like .ws, .in and country specific .com domains like .com.au aren't transferrable yet. The full list of transferrable TLDs is published here. There are also some cases where domains aren't eligible for transfer if they were registered or modified in the last 60 days. Those are all not big deals since this is a new offering and the list of TLDs and other features can only improve.
I run most of my domains on CloudFlare already and started to transfer their registration over now too. The cost savings are just too good. I don't foresee how any other registra could beat this kind of deal so my recommendation would be to follow suit...or just keep registra hopping!