I'm a one-man sysadmin / IT dept.
I started out with plain Xen on Ubuntu, but I've been using XenServer since the 5.x days in personal setups for the easier management tools, and for the last three years or so I've been converting a smallish software development company's infrastructure and dev VMs from headless vbox to XenServer. Orchestra was an amazing addition, letting the various dev teams self-manage their environments.
I'm really excited for the future of XCP-ng.