I held off on selecting a custom user name as I knew this day would come. That said, is this active for all accounts? The post didn't say it was being rolled out over the coming days/weeks. When you go to Profit - About - Get URL you cannot select any name. Am I missing something here?
FAQ still has old details: https://support.google.com/plus/answer/2676340?hl=en&topic=2400106