I've been using it now for about a year. Used to use Arch, but one upgrade broke the system (the perils of bleeding edge).
Sabayon is from Italy and is based on gentoo (without the endless compiling). It's a rolling release like Arch and I have gnome3 as my gui - have never really got on with...
Hopefully if it goes well, it'll roll out to more distros (thinking Arch, Gentoo/Sabayon here). Am I tempted to install Mint over my Sabayon install? Probably not, unless I knew the few games I play through Steam would work...