^If you want to check if a particular package is available as a binary in Gentoo/Sabayon Linux, you can check using the Gentoo Online Package Database:
Just enter into the Search box the name of the package you are interested in and all versions in Portage will be displayed. If there is a binary version in Portage then "-bin" will be appended to the package name. Here's an example for Mozilla Thunderbird:
Another way is to use Kuroo. Again, if you search for the package you are interested in and it has "-bin" as a suffix then there is a binary version available in Portage.
There are not that many binaries available in Portage because the philosophy of Gentoo/Sabayon Linux is to compile from source.
EDIT: I've just noticed that you can enter wildcard characters when searching the Gentoo Online Package Database so, for example, you can enter "*-bin" (without the quotes) into the Search box and a list of all binary packages in Portage will be displayed.