The Entropy method does offer one huge advantage over Portage though, and that is in full system upgrades. No more do you spend days rebuilding modules, python, and packages that need specific options set. If you have ever done a Gentoo world upgrade you know the pain and frustration that it can become. Entropy allows the whole process to be completed using only a single command that happens at the speed of your internet connection. Then if you want or need to, you can recompile the specific packages you want uber control of.
While the Sabayon crew will tell you, and rightly so, that mixing and matching between Entropy and Portage is dangerous and possibly system destabalizing, I have not yet run into any real issues with it. Mind you I only take fine grained control of specific packages that I use every day, such as wine and firefox.
The speed and stability of Gentoo are still present as well as it's incredible selection of packages and other associated overlays. Now this may sound like this is simply a more user friendly version of Gentoo, but it is so much more. It is one of the most out of the box functional distributions that I have ever experianced. From having Compiz-Fusion active even from the LiveDVD without the need for additional drivers, to the wonderful suprise of finding that my network attached printer had been detected and configured without any interaction from me at all and finding ALL my media immeadiatly playable.
There is also a great dirth of information available for it that is more controlled and professional than other distributions. The level of incorrect or out of date fanboi help and how-to's is minimal. While nearly all of the Gentoo documentation is applicable to Sabayon (and a nod to THE BEST documenation of any Linux goes to the Gentoo folks) there is also Sabayon spefic docs that keep to the high standards that the Gentoo community maintains.
If your interested in having the speed and stability of a Gentoo based system with the improved ease of use and management of modern desktop, perhaps better than most. Also having the Out of the box functionality that so many users crave with little to no mucking about with things after installation, give Sabayon a try.
For those without a DVD drive needed to install Sabayon, there is a CD sized installer that contains a very minimal set of packages, or alternatly you can use the how-to I wrote for installing the DVD without actually having a DVD drive by booting from the .iso.