Unless you like to tweak a lot, I don't expect you'll need to change the settings in /etc/portage/package.use very often.
As with Gentoo (since we're based on Gentoo), every so often, a package upgrades in a manner that requires an adjustment in the /etc/portage/package.use file. But I don't run into that too often.
Since SabayonLinux is pre-built for many possible environments, such as laptop, wireless, graphics driver, etc., Sabayon uses a more complicated array of USE Flags than the typical Gentoo user would set up. Due to the extensive USE flags employed, Sabayon also needs to implement a few more exceptions in the /etc/portage/package.use file than a typical Gentoo user.
But, hopefully, once the USE Flags are initially set up, the end user won't have to adjust them too much.
Gigabyte GA-P35-DS3L - Intel(R) Core(TM)2 Duo CPU E6750@ 2.66GHz
nVidia GeForce 7600 GS
2 GB RAM