Installed Sabayon_Linux_13.08_amd64_Xfce for the first time today. (And the second time, and the third time.)
Learned a few things that may help someone else. On the first hard drive I have the OS that came with the computer. On another hard drive I have Debian Wheezy stable already installed and it handles Grub2 (I have grub-customizer installed, nice program, allows you to change background, font size and more). So during the install, when I got to the boot Loader Option page, I de-selected install Grub. When the install was complete I booted Debian and updated Grub. The entrees for Sabayon appeared. Rebooted and selected Sabayon only to get "Kernel Panic-not syncing: Attempted to kill init!"
On the second install, the same exact thing. (I'm a slow learner.)
On the third install, I let the installer install grub, it had chosen to install to sdc. (sdb is a data only drive, sda is Windows) This time when I rebooted there was still my old Grub with no Sabayon, but after booting Debian and updating Grub, the entree was back. Re-booted and selected Sabayon and booted with no problem. So what I learned is that even if Grub2 is already installed, let the installer install it again. If you don't put it on the primary hard drive, you won't notice it, but it is still needed. I've never used a Gentoo based distro before. All I've done so far is adjust the desktop a little and install firefox. It seems to be very nice so far.