Erast writes "NexentaOS GNU/OpenSolaris is built on top of solid Debian/Ubuntu ground and enterprise level OpenSolaris core. Before Alpha 5 was released the only option to upgrade OpenSolaris core bits were to backup user's data and re-install new ISO. But not anymore.
Alpha 5 brings ability to perform OpenSolaris core live upgrade and significantly reduces the downtime associated with an operating system upgrade or maintenance.
It utilizes Debian apt-get remote repository capabilities, Debconf interfaces and marries them with BFU-like upgrade schema often used by Sun developers internally.
URL shows some screenshots of GNOME Debconf backend of the typical upgrade process."