Over the past year or so, Sabayon has really refined this technique. They get the absolute newest software from Gentoo Linux, and their primary developer, Fabio Erculiani, also participates in Gentoo Linux development, so he has a good understanding of how Gentoo Linux works, its advantages, and also some of its shortcomings. He has created Sabayon Linux as a convenient way to either update from the actual Gentoo Linux source code, or to update using already compiled and tested code, that he packages in the form of weekly updates.
I have found his approach to work very well. The only thing I'd like to see work better are the mirror sites. Only one of them performs well for me, and it's not always available to me. Fortunately, it is available to me today, and so I am taking the opportunity to upgrade my Sabayon system and work with it for a while.
So far, that has been proceeding quite nicely, and in fact, a rather large upgrade just finished. I am going to refresh the package cache, see if any other new packages have arrived, then check out the resulting system.